Serial numbers purchased now will of course work with the final release, and I don't expect SS2 to be in beta forever...
The point of open beta releases is to solicit feature requests and bug reports to ensure that final release is everything people want it to be.
If you feel it's not worth $25 at the moment, fine. But please do send feedback on what's there at the moment, and hopefully one day it will be worth your money. :)