If I turn off spaces on my MacBook, or reduce the number of spaces, will that improve graphics performances?
I'm running Mac OS X 10.6.7 Snow Leopard on a MacBook 7,1 with 2GB of memory
It all really depends. Truth is, you'll see some memory improvement in the spaces application and of course one less "daemon" running in the background. Switching to spaces is a GPU (and to some degree) CPU operation and also memory (both RAM and VRAM) is interacting in the process. Try disabling spaces and work for a few days.
You also don't mention your OS version or your amount of RAM. What Macbook do you have? Perhaps the best improvement comes from adding more RAM.
I checked it out in Instruments and I could barely notice a different in the activity monitor instrument, probably because I am looking at CPU and RAM bound items. There obviously is going to be a higher load on the GPU than if there were no spaces at all, but I doubt its drawing everything in all spaces at all times, and like Martin said, it all depends.
The real possibility is that with so much extra space that you run many other programs which in one space you would find cluttered and would have automatically closed them due to aesthetic reasons.