Chiming in:
Definitely with the people who are saying more rules != more imagination.
It's not to say that rules inhibit imagination, in a general sense... But I can't say that they facilitate, or even relate to it, either. When I see a Rgr1/Wiz10/Crazy PrC of Doom 4/Assassin 2/Oozemaster 1, casting Inexplicable Spell Which Causes Constitution Damage or something, and using a whole bunch of feats which seem to be entirely based on rules mechanics without actually making sense in the game world, the thing that comes to mind isn't "wow, what an imaginative player!"
As far as I'm concerned, player imagination shows up in three places:
- Character concept / role-playing. I'm sorry, but the books aren't going to help you there -- just get in the way. IMO Prestige Classes totally negate this: They're these very strict, comfy archetypes which aren't built to be played in any more than one way. Which is
fine: There's nothing wrong with wanting to play the archetypal Assassin, or Tomb Raider, or whatever. It can be lots of fun, and Prestige Classes are good for that kind of fun. I just wouldn't call it imaginative.
Further, extra rules screw with this even more by shifting you toward metagame thinking: With all the PrC's, you think more about "hey, look at how powerful a Ftr4/Mnk2/Duelist6/Guy Who Throws his own Head at You8 would be!" then "hmm, I wonder which classes would make the most sense for this grizzled old ex-gladiator pirate on a quest to destroy tyrrany?"
In short, when I ask for a character concept, and hear a list of classes (or class abbreviations, even worse), and weapons and feats, it doesn't strike me as at all imaginative. Which, again, isn't itself a bad thing, it just isn't "imaginative."
- Improvisation / in-game creativity: Again, rules won't help you here. In fact, they'll hurt: Having more spells means having more specific situations covered, having more game mechanics for certain situations convinces you to rely on those techniques rather than coming up with new ones (see the players who sit in the corner during combat making Open Lock checks when the key to the door was on a guard they took out earlier.) They don't outright stop you from being imaginative, and you can even use new rules imaginatively, but you can do the same with existing ones.
- Character design / metagame creativity: Which is to say, making a character that uses the game rules in a unique and interesting way. Again, I don't think more options really inhibits this, but I can't say it helps either. There are plenty of clever things you can do with the core rule books: Really, all that happens as you add things is that the clever things become more and more unbalancing. And, to a certain extent, less clever: It's pretty obvious that sticking a whole bunch of classes which get AC bonuses together will give you a really high AC bonus, and if you stop with that, you're totally missing stuff like a Barbarian who has Power Attack to use when raging, and Expertise to use when not (yes, not superbly imaginative, but I never claimed to be good at metagame creativity

)
...
Anyway, all this is
not at all to say "new rules suck!" or even "new rules are unimaginative!". Being imaginative really isn't all that important... Just trying to make the point that there really isn't much of a relationship between the two.