So you are denying that Vertical Farming and similar techs are more efficient for a Purity strategy than for other affinities?
Theres nothing that makes it more efficient for purity other than the fact that vertical farming is purity. You do not get any kind of penalty for researching vertical farming or using farms with other affinities.
If you are using farms, then you would take vertical farming regardless of what affinity you are.
You might even pick it up through spamming agents on steal tech. Its very easy to power through the tech web with that. Even if you dont, its what, 6 turns or so of research on quick speed by that point of the game?
Personally i always spam generators because farms are lackluster till vertical farming and high pop generates tons of unhappiness in BE. I believe its also easier to max out generators at +1 prod/+3 energy compared to farms at +2 food/+1 prod/+1 energy as well.
Most of the other improvements are unimpressive. You effectively pay 2 energy/2 health for +1 prod with manufacturies (compared to mines), biowells is basically 2 energy for 1 health, domes are 2 energy for 2 culture and some meaningless hp, etc. Generators are free and awesome.