Maybe this has already been mentioned, but the ideology system I think was designed to affect the game differently based on the galaxy you're playing. Since ideology points are earned only one of two ways - colonizing new planets or from buildings - then you almost always have a way to earn them. In a game where you can colonize 40-50 planets for your empire, you may not find it necessary to build any ideology point buildings. But what about a game where you can only colonize 10 worlds before you start running into neighbors? Then it's a value judgment - is the cost of ideology buildings worth the eventual ideology benefits. I believe that's why the buildings generate points so slowly. An ideology is meant to be an investment. At some point in your game, you won't be able to colonize anything new. Then it's up to you to create your ideology points.
I doubt many people are able to complete two or three ideologies by colonizing alone, unless you're in a very large galaxy with relatively few players. As Paul has said many times, GC3 is about trying to give the players interesting choices. And I think by limiting the pace and methods by which you can gain ideology points, you essentially have to forego pursuing all the ideologies and focus on one, if you want to get the best benefits from that ideology. That makes your choice of ideology interesting, not trivial.
I like the ideology system as it is now.