I'm glad this thread exists, but why did you have to go to non-core so much? Others have given better answers to some of these already, but I'm just gonna run through all of them at once, so I'll be repeating another poster at one or two points.
Misconception 1 "I am stuck with a bad choice in 3.5" ... contrary to popular belief WotC created retraining and rebuilding rules for PC's in the PHB 2.
Misconception 2 "In 3.5 skill checks are decided by one roll of the die." ...actually in Unearthed Arcana, there are rules for complex skill checks...they are almost the exact same rules (only explained in a more concise manner) that 4e uses for their revolutionary skill challenges. Seriously if you have the book read up on them.
Misconception 3 "3.5's skill system is too complex/fiddly" ...well again Unearthed Arcana has two alternate and more simplified systems for skills in 3.5.
Misconception 4 "NPC's have to be complicated and time consuming in 3.5." ...PHB2 actually has an appendix with a system for quick NPC creation, seems pretty straightforward and uncomplicated to me.
Misconception 5 "low-level Wizards are reduced to using a crossbow, once their spells are gone." Try using the recharge magic system in UA. They won't be hurling Magic Missile around every round, but they will be able to cast spells throughout the day. It's also really easy to tailor this system (adjust the recharge times for what one considers especially unbalancing spells) for customization in one's campaign.
Well these are just 5 so far...might come back and post some more later. Also, if there are any problems people are having using 3.5, feel free to post them and maybe there's something I come across that may help you out.
1. Some options can be changed, such as sorc and bard spells known. Aside from that, a DM doesn't need retraining rules to have some mercy. If someone's really not happy with their choices, I'll let them make changes. I came to this opinion long before PH2 or DMG2 or wherever the rules first appeared. Rule 0 trumps all. If your DM refuses to budge at all, there is still a "core" method to fixing this -- get your character killed, create a new one (likely a level lower) that's very similar built the way you like, and problem solved. Is it silly to go to such lengths? Definitely. That's why it's better as DM to just lighten up a bit. But the fact remains -- this option is completely "core."
2. Often times there will be situations where it takes more than one skill check to accomplish something. A bargaining session could entail several diplomacy checks. The search checks merely opens up a bunch of new checks -- disable device; balance when that fails and most of the floor falls away; climb to catch yourself from falling if that fails; tumble to reduce the falling damage if that fails... whatever, just one example. The DM creates the environments and challenges. He doesn't need complex skill check rules to make a scenario that involves several rolls, and (gasp!) maybe some roleplaying, too!
3. I know someone said this already, but for [insert your lord's name]'s sake! Pick x number of skills you get per level by base number, int, etc... and choose that many from your class list. They are always ranks = level +3, and...done. NO different than picking your trained skills in 4E. If you want a more fiddly character with ranks all over the place...that's your call. The system in no way forces you to do this, however, and you can choose to emulate 4E's "trained and untrained" binary dichotomy if you wish.
4. Technically, any creature controlled by the DM is an "NPC," not just the ones with class levels... In any case, once you know the costs of the "big six" items types and look up the classed NPC's gear value, it's not that hard to give them the standard stuff. If you want more diverse things, it will of course take longer to add up. I usually just give the guy a rough estimate of all the things I think he'll "need" in what i think will come out about right for his gear value. Then I quickly add it up with rounding (I would count a +2 sword as 8000 gp and not bother with the base and masterwork cost, for example) and see about how many thousands of gp I get. If it's about right, awesome! Done! If not, I take the rough values and start removing the "least important" things or reducing +'s. It's really not that hard, the final value can be ballpark, you don't have to hit the exact number.
5. Someone already said how 3E crossbow isn't much different than 4E magic missile. And unlike 4E, a lot of spells have LONG durations, so while a 4E wizard has a hard time finding many all-day effects, a low level mage can have mage armor, unseen servant, mount...and that's just core conjurations of level 1. It may not be sexy, but getting that +4 AC for the entire dungeon sure is nice. Others said how the player can still participate in non-combat encounters and hel out with bright ideas and support (aid another?) in combat, so they're never worthless. It's also unlikely they'll run out of cantrips as well, unless the DM is really taking it hard on the party. Prestidigitation lasts an hour and can be used in innumerable situations. Ghost sound can set up an ambush or lure away guards. Message means you can fake being unconscious face-down and continue communicating with your allies...umm...kinda random example, oh well. Point is, seldom will a low level caster ever actually be made useless.
Here's a misconception I want to add:
6. 4e improves on 3E because you get better at skills as you level, even if you don't put ranks in. Err...train in it.
Answer: First of all, I consider not giving people good skill checks merely from being high level to be a GOOD thing, so this is a matter of taste. I really like that a level 1 expert who's never fought in his life but made weapons for 20 years can still craft better thana level 20 PC who's never worked in a forge a day in his life.
Even if you're appalled by such a possibility, do realize 4E is a false solution. In 3E, if two level 14 guys have 0 ranks in a skill, they both have +0 before other modifiers. In 4E, if they are untrained in the skill, they have a +7 before modifiers. So, if they're rolling opposed, the net effect of 4E's changes is...nothing! "What about for fixed DC's?" you ask? Well, see that's where 4E's focus on balance bites it in the ass. Sure...at level 14 you can climb that thick silk rope much easier than you could at level 1. But at level 14, you won't likely be seeing that nice silk rope. The rope in front of you will be covered in grease to keep you paragon folks from easily scaling it. you've done nothing on your own to improve your rope climbing skillz', so you're just as screwed now as you were then. NO CHANGE from 3E.