Did anyone experience if using Spaces slows down the system? Is there are difference between using 4 spaces vs 9 spaces?
Although there is some very tiny overhead tracking the views of 4 or 9 windows - and your graphic card may be stretched to render more than X items at once - so it feels slower and renders slower animating the in/out of the spaces.
As far as the apps and the system - each window that is running simply gets coordinates. If it's marked on screen 1 and offset X and Y or no screen and X and Y - the system does no extra work. Each window must be tracked and only windows that are somehow visible get refreshed. Spaces adds no extra work or saves any work as far as the application is concerned.
If you tend to open more apps due to spaces organizing them - that will slow the machine down - but it's not inherent that spaces makes anything on the system or app level slower other than an added graphics drain to animate the changes. When you are not switching - it's probably faster since fewer windows have to draw into active viewports if you have less "on screen" at one point in time.
I'm using 9 spaces and here is my own experiences:
ps: these are my experiences, others may have other opinions.