Re: Making colonization attractive?
Fine. Except there wouldn't be a colonization effort, unless it made very good sense. That's where the logic comes in.
Scientific outposts are more likely, since they aren't required to be self-sustaining or profitable. Some of these might theoretically form the basis of colonies in the longer term. In the immediate period, though, the personnel living at such outposts are going to be handpicked "best of the best of the best" types.
Unfortunately for game purposes, there are only a certain number of scenarios you can really set in such outposts. That means that a game would have to go off on a funky tangent to be interesting. Which is great, of course.
Incidentally, interstellar colonisation without FTL is extremely dubious. Any colonisation attempt that wasn't preceded by an extensive program of investigation would essentially be a suicide mission, and STL timelags make such investigation extraordinarily time consuming and complex.
Of course, if you had a society that was happy to live in artificial habitats, and not on planets, you wouldn't necessarily need to investigate colony sites, apart from finding sources of raw materials.
But artificial habitats would have all the charm and adventure of living in a remarkably small city, at a remarkably long distance from anywhere else. They are the kind of place adventurous spirits would want to leave, not live in.