I won't get any updates to the beta? Just the current version and the full game?

AFAIK you get all updates for free until (and including) the "final" game.

You'll get all updates up until the game is released, and you get the release version but no updates after that (bug updates is, of course, an exception).
From Notch's blog.

It's still very much worth it.

You should have bought it yesterday. 
 
The way I understand it is alpha owners get everything with the name minecraft on it forever, beta purchasers get everything up to the final release but no expansions or anything.

You'll get every Beta update since the game isn't out yet, obviously. After it's released fully though, you'll only get so much as bug fixing updates and such. Larger additions, such as any expansions, will be free to Alpha users but not to Beta+. Makes me glad I grabbed it for $15 in Alpha, and it was totally worth it seeing how much of it I play.

I think you can buy it right now and get everything you want out of it. After a few days of mining it tends to get old. You can appreciate youtube videos of crazy people's worlds but, let's be honest we play a lot of games and don't have the time to spend weeks mining for gold.

" I think you can buy it right now and get everything you want out of it. After a few days of mining it tends to get old. You can appreciate youtube videos of crazy people's worlds but, let's be honest we play a lot of games and don't have the time to spend weeks mining for gold. "

" You should have bought it yesterday.  The way I understand it is alpha owners get everything with the name minecraft on it forever, beta purchasers get everything up to the final release but no expansions or anything. "

I'm thinking about buying it and had the same question as OP.  It looks neat but I'm still on the fence.

Get it now. You will have more time playing it, and it will cost you less than buying it when it goes final.
 
Unless you're the sort of person that don't know what a beta is and will complain about how unfinished the game is. If that's the case you could do: A, buy it now but don't start it until the game is final. B, buy the game when it's final but at a higher price.