I've never really found the Culture to be that optimistic. The people are basically pets, the vast majority of which seem occupy themselves with vapid shit, and the "important" jobs humans have are actually unnecessary (as the "Minds" can do everything better).
I thought the Gzilt from the last book had a better path of development than the Culture. It seems they took every opportunity to keep humans (in some form) in control at every level (e.g. no "Minds" on their ships, just groups of emulated humans running at accelerated speeds to achieve the same effect).