Play slow, don't conquer too fast. (Of course this is hard, seeing as the AI conquers fast and if you don't you die.)

Eventually you'll get all the buildings in your towns and won't have to worry about that. I usually will do administrative things once a year (spring), such as moving around governors.

I know how you feel though, I moved up the Marian Reforms and ended up getting them in 199-195ish. And the Imperial in 130ish.