What that guy said.
But since I'm in a good mood, I'll help you out a bit.
The WhiteBook and alu MacBook have the same graphics card, just that the alu one has DDR3 and the white one DDR2, so the difference in performance will be a bit different. Even if you don't play games, a good graphics card will make your overall experience much better. The build of the alu one is 1000 times better. I have had the casing on my WhiteBook replaced once (I have it for a bit over a year) and i already have 4 cracks on the inside, and I baby this thing like nothing else. Also, like you said the alu ones have better heating.
I think the price difference is way more than worth it for the alu one.
I tend to agree that aluminium is nicer, BUT having dropped my MBA (not very far, in a case) and seen it bend when plastic would probably have just been fine, there are pluses and minuses. The plastic scratches more and creaks more, but it's still pretty sturdy and is probably less susceptible to damage from minor knocks. Assuming it doesn't crack, it appears fine, where as aluminium bends I really don't know. I just know that I've seen friends drop white plastic macbooks in a biiiiiiiiiig way and they came out of it better than my Air with its much smaller drop. The macbook should be a bit stronger, since it's that bit thicker. It does indeed not dissipate heat as well. The actual performance between the newly up-specced white macbook and the alum one should be fairly minimal.
You would probably be well advised to check out the screens side by side too. IMO the white macbook is actually nicer due to being less reflective, though many people like the new ones more - it's probably a personal choice thing so I really would take a look if you can.
One other note, the keyboard feels more solid on the aluminium ones.