I cant say much about the ethics. Usually when I get to that point in the game, i'm more concerned with an End-Game. However I read some stuff recently about rushing that tree (especially if going neutral for the research and shipping improvements), so I might experiement soon.

Personally I have not found power plants to be a very good buy. I dont usually make "mega-super-production-planets" like some people do. So when I look at the % bonus I get for a power plant, it's usually better to get a factory instead. (or at least very close)

Because it's a % bonus, the more factories you have on a single planet, the more sense it makes to get a power plant.

I ended up liking the change here in DA. The terraforming bonus isn't gone, it is just linked to your tech tree.

Now you have to develop a given terraforming tech before you get the "extra" squares. (They're not extra for Neutrals, they just don't cost anything to make habitable.)