Edit: You seem to have edited your post a lot since my reply, but here are my responses to the original.
Why on earth do you trust Maxis to do what's best for the game?
As far as games companies go, I've never had any reason to complain about Maxis. Speaking mainly of their games that actually appeal to me (not too keen on The Sims but I have dabbled in it), they've all been very good games. Watching and reading interviews with Will Wright, in my mind he easily ranks up there at the top as far as far as being passionate about his own games goes.
And how can you not see that the gameplaying style and behavioural coding of the creatures is completely different? The creatures were clearly given completely different AI, one that reacted to the environments around them... this would have changed the game massively!
I can't say any of that because I am not a developer at Maxis, but based on my own observations he AI in Spore does react to me based on my actions toward it.
For example; In the "civilisation stage", playing as an economical species, other cities reacted pretty negatively toward me for growing too fast or for dealing with cities they didn't particularly like. Laying off on trading with those cities, or giving bribes and more trade, changed their attitude toward me for the better.
The society evolves from a SINGLE gamefield... there is no ridiculously simple sub-seciton for each stage... it's completely seamless... this also would have been a huge change to the game! And did you see the space section?
I'm pretty glad it's in stages because, once you complete a stage, you unlock it and are free to go back to any stage you like. Personally I wouldn't like having to start from the cell stage just to play around on the civilization or space stage for a while, just some obvious tailoring toward the casual gamer audience there.
Edit 2: I'm going to try to isolate and reply to the new bits: -
In the 2005 version the creatures design massively influenced their behaviour... long legs faster, short legs slower etc etc... this would have made for a COMPLETELY different game in those sections instead of the stat-based simplefest it is now.
You can still adjust how fast your creature is simply by choosing feet suited to the task. In the 2005 presentation I saw no way to stop you from simply adding loads of legs with a huge stride and being fast as a cheetah on E, and even then it would've been a stat-based system, just running in the background instead of in your face. Yes, it is simpler, but like I said, this is a casual game aimed at ages 10 and up.
otherwise why the hype about making your own creations? That's what was originally intended as a major selling point of the game.
As far as I'm aware there's no game on the market that lets you be as creative as Spore, even in its current state. You can poke and prod, and build and design everything you use in the game in your own image.