The problem with orbital habs is that they have a crew morale requirement now just like ships. And they're a hell of a lot harder to move. I suppose if you didn't mind it being OMFGbig, you could build a recreation module into the orbital hab, so it would have unlimited "on-station" time. But then you're talking probably 300,000-400,000 ton range. Which means either building a bigass tug or putting a ton of engines on it, and either way it's going to craaaaaaawl.
I typically make my long on-station vessels like terraformers, fuel harvesters and asteroid miners to be 100,000+ ton ships with a crew duration of say, 1200 months. Although lately I've been going with a design philosophy of making those into engineless "platforms", which are hauled into place by tugs. Otherwise the engine and fuel requirements become substantial, which adds to the crew, which adds to the tonnage needed for maintaining that long crew duration, in a vicious feedback cycle. I can shave a good 30-40 thousand tons off just by dropping the engines and fuel. And then I never need to upgrade the design again (unless I just want to make the armor better).
Gets to be a bit micromanagement-heavy with all the tugs, but not too bad since once they're hauled into place they'll be there for decades.
I just don't find orbital habitats to be efficient in any role. PDCs are better for military role, automines + mass driver for resource extraction on uninhabitable worlds, and terraforming ships for terraforming. I suppose in the last one, planetary installations are considerably more effective than shipborne ones, but the number of population required to run them mean that you have to build a mammoth orbital hab to man them, and the total build, mineral and fuel cost is more than likely going to dwarf what it would cost to build several terraformers to do the same job.