If you look at my earlier post...
It's all a question of maintenance as you say, if devnull does that (90% reduction) then it would definitely pay off. I have used it extensively in stock 1.49, but then I always max my maintenance reduction.
Build a decent-size ship with stellar harnessing panels on board and it will sit there making a profit until some rude stranger comes and shoots it. If you use ships and not bases you can of course run away, or, in a long game, move it on once the resources run out.