In the grand scheme of things, I bought Starsector only recently. I bought it in May. Of 2016.
Alex can of course correct me if I'm wrong, but Starsector was first available for purchase in 2011, as Starfarer. Since then there have been multiple releases which have changed the game in very fundamental ways, and in my opinion, for the better. I have confidence Alex is working on the game because he has an excellent track record for the last 10 years. The updates are slow, but that is because the development team is tiny and the releases are high quality and significant.
Everyone has different levels of preference in time versus quality of updates. Or how finished the game seems to them. I can understand why people might be worried about year long gaps in content. I personally don't worry.
In my case, I've gotten far more entertainment out of starsector than many other, more expensive games. I always find myself coming back every few months or so to check out how mods have evolved or if new ones have popped up, which can certainly scratch an itch for new content. So even if development stopped today (which it has emphatically not, based on all the cool twitter graphics I've seen in the last few months), I'd have considered the purchase of the game as well worth it.
I mean, back when I first got into computer gaming, you bought your floppy disk copy of the game and that was it. You didn't get updates. This "get good game now" and "get better game later" is a rather new fad.