I haven't been playing as long as you have, but the bold section has not been my experience. For the first 3 levels, yes, I agree. Somewhere around turn 50, I usually decide what affinity VC that I intend to pursue.
- If I have enough land available, so that I could easily settle groups of Earthlings and build magrails, I go for Purity. If it's more of an archipelago map, with my cities on smaller islands and aquatic cities, I avoid Purity
- If I have an excellent science rate, so that I could get all 3 final techs, I go for Harmony. It's one of my favorites, in my avatar
- Otherwise, I go for Supremacy
Once I've made that decision, I choose techs to get me the affinity I want. My games have been something like 15, 6, 4 in the other affinities; or 15, 7, 7. My goal is to reach level 15, build the manufactories, and research the final tech about the same turn.
Only occasionally do I need to mount an invasion to destroy an AI beacon being built.
If I'm going for Domination, that's part of my planning from turn 0. My choice of sponsor, my choice of loadout, my choice of planet.
It would be a fun challenge to get all the affinities to level 15. I'm more focused on trying to get the achievements for all the virtue synergy bonuses. My habit (or is it a crutch) is to take nearly all the virtues in Prosperity so that my Health stays green through turns 100-200. By turn 175 or so, I've built enough buildings and taken enough virtues that I'm permanently healthy.