I agree with Keenath.
Unlimited surges gives them the ability to use a few each fight over multiple fights. They can still only use a few surges each encounter though, unless you're giving them backpacks full of potions - a clear "no-no" in your style of campaign.
Another factor that might make them fear no monster is that they can nova their dailies. This has been said, but the people saying it are almost unanimous that you are making a mistake having just one encounter in a day.
I also like city adventures, or wilderness adventures. It's hard to reconcile that the 5 days of travel on the road from Tarnaq to Mar'Delenne will be frought with 25 encounters. How would merchants, or even military patrols, ever survive?
Yeah, maybe POL is like that, with constant danger between the L's. But I don't play POL. My world is more civilized, more orderly.
Which means if I want a kobold skirmish on day two and bandits on day 5 of that road trip, I will have to deal with novas and with the PCs have more surges than they can possibly use.
Which means either turning the kobolds into trolls, or having many dozens of kobolds, or turning day two into a slug fest with 4 or 5 encounters literally coming out of the woodworks.
None of those answers is really satisfying.
It's no different in city adventures. OK, so today the PCs will get into a brawl in a tavern. But, to make it a challenge, they also must face a vampire before dawn, rescue an orphan from wererats in the sewers right after breakfast, bust up a gang of thieves after lunch, and help the city guards turn back a marauding band of ogres before dinner - now they're ready for the tavern brawl to be challenging.
How can anyone live in a city this dangerous?
/sigh...
So the only satisfying answer, to me, is to break up the routine in lots of ways.
1. Some encounters are bigger than the look at first. Maybe the kobolds send in 8 or 9 minions and a leader to test the defenses while the other dozen kobolds are hiding. The players go nova, wipe out the expeditionary force, then the rest of them burst out of hiding. Not even a short rest here.
2. Maybe sometimes the kobolds and the bandits attack on the same day. Too bad the PCs used their dailies on the easy kobolds this morning...
3. Sometimes using trolls instead of kobolds really is an option. Make them earn the victory, blasting every daily, encounter, and surge ability they can muster, and still having to wake up half the party from near-death when it's over.
4. Sometimes the enemy skirmishes. Hit and run. Ride by, pelt the group with arrows, run away and scatter. Watch the PCs heal, then skirmish again. Sometimes skirmish at the 3 or 4 minute mark, interrupting the short rest.
5. Sometimes the extended rest gets interrupted - no dailies are recovered. Even more humorous if it happens right before dawn, say, at the 7th hour or so - now the PCs have to fight some harmless little minion, or trivial encounter, but there is no time to lay down for another 8 hours, so better be careful today. Maybe should have saved some dailies from yesterday rather than going more nova than they had to...
6. Maybe there's some EvilGuy (tm) who knows about PCs, knows they're becoming a danger to him, and knows how the world he lives in works (dailies, surges, etc.) as well as the PCs do. Maybe he deliberately arranges timely interruptions to their happy schedule, deliberately depriving them of resting opportunities, deliberately tempting them to blow dailies and burn surges on the EvilGuy's (tm) weaker forces, all the while saving up the main strike force to swoop in and TPK while their resources are depleted (he plans the TPK of course, because he's an EvilGuy (tm), but hopefully your PCs foil his plans).
Doing all of this stuff, and mixing it up, will quickly teach your players to save their dailies.
I'm not saying do this all the time. Don't change your campaign style. Have your one encounter some days. Just mix this kind of stuff into it so the players never really know if today is a One-Encounter-Go-Nova day, or just the beginning of a Three-Days-No-Sleep-Save-Your-Dailies marathon.
After all, nobody recruits a pitcher who can only throw fast balls. Gotta pitch them some curves and knuckles and sliders and change-ups or they'll keep knocking your monsters out of the park.