Yeah, I've encountered this as well. I barely ever feel like playing now because it all has a been-there feel.
But I'll bet I've spent at least 100 hours entertained by the game so far (without mods). That seems like insanely good value to me; at least 10 hours per dollar! (5 if looking at full price, still good! And more content coming means more hours).
For comparison: I've played (good!) singleplayer AAA games that barely got me an hour per dollar. Indie games I like, I tend to get closer to two or three hours per dollar spent.
In that respect, Starsector is doing quite well. I could put it down forever right now and never regret the purchase
You're gonna get bored with a game at some point, that's inevitable. But did you get enough out of it before that? I'd love to find a game that's infinitely replayable, but that just doesn't exist (not counting mods and updates).
That said, there's always room for improvement. Luckily, there's a list of upcoming features that seem to address this.
I fully expect to be able to squeeze quite a few more hours out of the game once it's complete (and/or before that, I'll probably spend a good while poking through each update anyway).
In the mean time, I do hear mods are quite good so maybe I'll try those while I wait ^^
