"Buildings are cool"
I think we should have buildings, in general. Most people are familiar with buildings, and buildings add to immersion too. I alwas liked the planet/city view screen in games like MoO2 or Civilization. And I really missed that in MoO3.
They got boring especially in MoO2 in late game when every planet had nearly every building anyway, but that doesn't have to be the case in FO. That's why I think the amount of buildings should be limited somehow, by a number of slots for each planet size, by technology level, or by population count.
Good buildings, bad buildings
Buildings in general open up many development possibilities and choices. And add a lot of functionality you could expose for use in mods.
And add lots of cool possibilities for the thech tree

As long as there are really choices/trade offs to be made. So, as drek said, it's boring to have a "mega farm" that's
always good on farming worlds, at least if you have to build it manually.
That could be considered when designing the actual buildings though, designing buildings with high maintenance so it's no use to have them on small/unimportant worlds. You could also design buildings with very high initial production cost, that take a very long time before they pay off.
A good example of how not to do it are buildings in MoO2 like automated factories: They make workers more efficient, which is ok. But they also add some automatic production, which is bad, because that is enough to justify their maintenance cost, so you just build them on any world. If they would
only increase worker effectivity, you would probably build them on industrial worlds only. If their initial production costs were very high, you probably wouldn't build them on low population planets, or planets lacking good defense (because of the risk you could loose them to your enemy).
Choices to make
But I don't like automatic construction of focus buildings or infrastructure either. It cuts down the available choices.
For example, I may have a large, important world I use for ship construction, basically the backbone of my military industry. It will focus on industry, of course, and have lots of defense (or, if it's in, defense as secondary focus). But it might be a good choice to place a few basic farming/mining buildings there, so it stays functional to some degree when blockaded.
Building prerequisites
I like the idea that some buildings can only be built on planets with a certain focus. But it shouldn't be like this for the majority of buildings, just for the more advanced ones, so you could still place a few basic farming buildings on an industrial world, as in my example above. You could make this to be relative to your current tech level.
In general, I like the idea of having prerequisites for buildings. I can think of more applications for this than focus prerequisite, maybe some buildings for large/small planets only, buildings that require other buildings, or mabe some exclusions ("Building X" can't be built if there's already a "Building Y"). I don't have good examples now, but it would at least allow us to be very creative when it comes to designing buildings
Micromanagement=bad?
All over the board people are condemning micromanagement, trying to get rid of it for FO. Micromanagement
is bad when you have to do it all the time for a large number of worlds. But I think there should be
the possibility to micromanage. So in general, I'd rather like to see a tool to handle micro effectively, than eliminating it completely.
The ability to issue a command like "[Enqueue on top] [automated fatories] on [large] [production colonies]" in MoO2 would have been sufficient for me.
Still drek convinced me that it's better to eliminate the tedious "no brainer" micromanagement completely instead of simplifying it. But that can be accomplished by limiting the number of buildings on a planet, good building design, and introducing building prerequisites. So there
is micro management, but it's interesting and you don't do it all the time. The choices you make really do matter. No need to leave buildings out completely.