I've only played one game so far and it was with 7 players so that might not have been a normal experience...
I got the feeling that most cards in Age 3 are simply not affordable because they need so many resources.
- Is that a common thing, i.e., you'd have to deliberately focus on resource cards if you want to build a lot in Age 3?
- Is it just bad playing on the part of me (and others)?
- Maybe it's even an effect of having so many players?
EDIT to elaborate on my experience: I actually won the game so there's no complaint there. I had around 4 brown/gray buildings and my neighbors had roughly the same amount. I don't think I had one of those yellow free resources cards though. When Age 3 came I realized that about half my hand was impossible to build because neither me nor my neighbors had the necessary resources. I eventually relied on the few cards I could build and a lot of freebies from previous cards (I think I placed about 5 buildings for free). IIRC I never trashed a card in the last age but I did build my last two wonder stages...