To answer OP's question - last time I looked, there were 7 servers, with one dedicated daytime server (which is most evenings full), and all of them have players on them. You should be able to view the player traffic on gametracker.
I contemplated about 2 weeks whether I should "invest" the $30 and my time into an alpha/pre-alpha and eventually bit the bullet last week. I've put around 8 hours of game time in and still find it enjoyable with still lots of places to explore. I'll be honest and say that it is a bit frustrating, at times, with the few bugs that I've encountered, i.e. glitches and random slow performance. Once they start releasing new features, especially base building it'll become even more enjoyable.
Zewp, out of principle, I agree with you on the development timeline (or lack thereof), but after going live on steam, I suspect (read: hope) that the pace on development and releases will increase. They've got sufficient funding to get things done now and a player base that'll nag them for new features and content.
So, OP when/if you buy it, you need to fully understand that the game is incomplete and has bugs, but you'll get early access to a playable game (and possibly at a cheaper price).