3.5 streamlined a few problem areas. For instance, it took a few of the really overabused spells, and fixed the abusable parts. The folks I've heard complaining the loudest, appropriately, are the players that are always looking for a loophole to exploit to guarantee their character is better than yours. There's one at every table.
The closest thing to 2e kits are prestige classes, which were introduced in 3e. Some of the more popular ones from expansion books were stuck into the 3.5 DMG, but other than that nothing really changed.
Two other significant changes: the combat rules in the Player's Handbook got a bit of an overhaul, streamlining some of the more difficult-to-understand options... 3e at large is entirely more tactical than 2e. It doesn't mean that it is focused on combat... it just took something that was kinda rough and freeform before, and makes it easier to visualize. (Beauty of it is, just like any other ruleset, that you can choose not to use the tactical part of the rules in your home campaign, if it doesn't suit you).
Second, the Dungeon Master's Guide got a huge section filled with tips and tricks for DM's, and a lot of common sense guidelines. A real good read for a fledgling DM.
The cost of buying new books? Phhh... 20 bucks to buy a new PH. It costs more to go out for a night of drinking, and you'll get much more value out of it. A gaming group only *needs* a single copy of the DMG and Monster Manual between them... it was easy enough for everyone to chip in for a set and share them, until people felt like getting their own. A few of our folks still only have the PH.
