You basically pay 25 extra dollars for early access to a demo of the game. If that doesn't sound too outrageous, then you may find it worth it. It just depends on how patient you are and how enthusiastic you are about supporting the development. There's certainly enough content and opportunity for emergent gameplay in the game already to keep people busy until release.
I don't regret my purchase, but I am impatient, financially irresponsible, and very enthusiastic about this game. The perfect customer. Fortunately for me, the game is still extremely fun in its current state. So I hope that answer is as ambiguous as possible.