Oh yes, it adds huge amounts to a scene! What I meant more was that it (afaik) cannot really be scaled down to run well on older systems while still looking nice. Of course, that depends on what is meant by "older system". But CSM gives you more room to play around and provide a variety of options, I believe (although I have no actual experience with SSAO, so I could be completely wrong).
Cheers I look forward to seeing how much you do with it.

Jibb