I make my parties rest after combat encounters, because real combat is exhausting - whether you are lugging sixty pounds of gear and a sword, or 90 pound rucks with modern combat equipment.
Combats (or fights in a game sense), are exhausting both physically and mentally.
But you don't sleep after a good fight, that's the last thing on your mind because of how wired you are from a real fight. Resting to regroup, counter, getting water or liquids, recovering one's normal senses (in combat or even near combat - where you are certain you will fight but it doesn't actually happen, when you're wound but never sprung or cut loose [actually being wound and never spun out is worse than a real fight]- one's senses become enhanced and then it takes awhile to come down again and regain a sense of normality and to regain your ground strategically and psychologically, rather than remain at point focus for tactical preparation or reaction), and so forth is really necessary if fights were real. Of course it's just a game, but of you think back to your own best game fights then you as a player will realize that you have probably also had intense periods of focused tactical concentration, where everything else in the game is forgotten while you concentrate on the combat situation at hand. (This is an excellent time to execute a staged ambush against a party as well, because of that sense of focused tactical consideration.) Now imagine the stress and strain of real combat, coupled with focused and extreme tactical consideration, the fog and disorientation of combat, and the possible psychological shock of injury, and the very real potential that you or your buddies will lose your life. then imagine it's not a game, but it's real. Well, if it were real then that's what the characters would be experiencing. Every combat encounter.
It's draining. To say the least. So recuperation is necessary, or would be if it were real.
Same for basic slogging. Carrying around gear, pack, weapons, etc. is draining and after a good hike it stiffens the body, slows the reflexes, taxes muscular strength and endurance, and weakens concentration. Therefore if it were real then rest would be an absolute necessity. I hike in real life and so I know this is how it is. The more you carry, and the farther, the less prepared you become to shift gears for combat and other surprises.
I also vad (what is today called urban exploration, though I also often explore rural or industrial ruins) and so I know from first hand experience, especially at night, that exploration of unknown sites and the possible dangers you must prepare and be on guard for, is also taxing on mental and physical resources and capabilities. You cannot simply walk into an unknown and uncharted area, anticipating danger, and breeze through it. Progress is slow, methodical, and exhausting if done correctly, and with the intent of avoiding, rather than merely enduring, catastrophe. And it is always better to avoid than endure catastrophe. If you make a mistake you might not recover or you might be so severely injured, by nothing more than negligence or failure to anticipate danger that you could become incapacitated. That might not be so bad if you could whip out a quick "cure everything spell" or a "mister miracle potion" but in real life it is also a daunting prospect - what could happen cause you're stupid or unprepared. So I make my party rest or regroup accordingly. Exhausted = stupid. Prepared = capable.
They never sleep without watch, because to do so is suicidal and asking for ambush and/or for an enemy to attempt sabotage, or worse. At the very least they could be easily surveiled or reconnoitered without even being aware that they were being targeted. And yet they must sleep. Rest is necessary. Necessary to regain physical stamina, necessary to recover mental concentration and focus, to heal from injury or exhaustion, to regain psychological control of temper and adaptability, and so forth.
However because of personal experience I also know that when one is in a dangerous environment, either purposely or accidentally, it stays in the back of ones' mind during all operations and activities. You never really rest in a completely relaxed fashion, you sleep lightly, your senses are highly tuned, your reflexes are primed, muscles stay basically tense and coiled, and so this gives a reactionary advantage, at least for a time. Eventually however always being on alert, even if just subconsciously, will lead to real exhaustion, dehydration (unless one is very careful), injury, unwarranted aggression, unnecessary mistakes and susceptibility to disease. Everyone will be affected differently based upon their own state of preparation, resistance, and experience to such situations and rates of exhaustion will likewise vary, but eventually everyone will succumb if the condition persists long enough.
How these factors are translated into the game is of course up to every DM, and since I don't really play the 3rd Edition game I can't say how, or if it is. I have adapted certain game mechanical aspects of that system to our game but as for other aspects we really mostly play 1st edition and leave situations like this open to the most realistic manner of depicting them possible,
Since a lot of us (my buddies and my players) have personal experience with similar conditions, situations, and/or training most of my players just personally understand how these things work and we don't really look at enforced rest as "regaining spells" or magical whoop-ee-dupe. but as a biological necessity of physical limitations during an operation/mission/venture. So my players rest because if they don't then I begin to penalize their reaction time, stamina, strength, reflexes, resistance, etc. To simulate what would really happen in those conditions.
What that really means to your concerns, I'm not sure. I guess it's up to you and your players. I'm just describing what we do.
On a side note I will say this much, since you eluded to the same basic theme: playing AD&D was very helpful to us when we were still kids in developing real world skills and understanding resource capabilities, deployment, and applications in any given situation. It helped prepare us for later training and activity where it became vital in the real world to prepare well ahead for nay particular assignment, mission, scenario, or even wargame training. So over time I developed, with the help of some of my friends, a hybrid of the game which stresses development of game skills and capabilities which mimics real world situations, and vice versa. That is to say we played the game as training for the real world and later sort of transformed the game to reflect the real world so that in-game scenarios became role play training for real world situations, and vice versa. So that the game (as much as possible given the limitations of the game) became training for possible real world situations, and the real world started to become more and more reflected in our games. My buddies and I often have had discussions about how the game prepared us for this or that thing in the real world. Not of course the ridiculous in-game elements of meeting fairies or slinging fear spells from rods of lordly might, but things like how can we use this spell or that piece of equipment or this bit of intelligence to prepare to maximize our chances of survival, or to anticipate this or that disaster. We leaned valuable tricks (and developed a few of our own) regarding ambush, tactical combat, the achievement of strategic objectives, sabotage, logistical supply lines, exploration and mapping skills, manhunting and tracking, spying, surveiling, gathering intelligence, filtering Intel, command and control, deployment, curtailing criminal activity, group and individual security, escape and evasion, pursuit, translation, communications, codes and cyphers, psychological warfare, leadership, disaster preparation and recovery, and so on and so forth.
I was very disappointed that the 3rd edition, which showed so much premise at first I thought, by incorporating skills and feats to a complex level eventually degenerated into a kind of superhero game and lost it's emphasis on survival and the imaginary and yet more concrete development of real skills which are theoretically valuable when applied to the real world. The later editions of the game became more and more about describing cool new sorts of outlandish skills than developing practical and useful ones which were kinda natural and intrinsic to the original game. Because the original game was less about "power" and escapism and more about survival and achievement and the exercise of practical and useful benefits conducive to real world success, at least in some situations. That's my opinion having observed the game for a long time.
I'm hopeful the new edition will move back more towards this older ethos of practicality and usefulness and away from the totally whiz-bang, "look at me, I'm a superstar" elements.
Now if you'll excuse me I've had about 4 to 5 hours sleep over the past 38 to 40 or so and being an old man (to many of you no doubt) I'm too exhausted to even properly edit this post.
Anyways, good luck. And good night.