I think this is an interesting question - I think of SS2 as "game within a game" - the objective being to build up your settlements as much as possible. Try to get the plots to level 3, unlock the higher levels of the tech tree, get neater and neater stuff to add. In this sense, it is like civilization or sim city where the end objective is try to get as developed as possible. And yes, it will unlock certain content that you will not see or experience otherwise.
If you're looking at this solely as "how do I make more caps" - as many have pointed out there's a lot more straightforward ways to do that in the game than through settlements, and even within settlements you would be better off trying to become a water baron or glue baron. Or, as you've pointed out, try to run the nuka world raiders and just take over all the settlements and collect from your tribute chest. In general, though, you'd make more caps just running a dungeon, picking up the loot, and selling it than most activities in the game. Of course, I'm the opposite. More often than not I'm scrapping all that loot, donating it to the city planners desk, and spending every cap I have on junk, which I also donate to the city planner's desk. It's all about what you are trying to achieve.