I don't see how you can actually decide to continue messing around with the Demo version, instead of paying out the $20 for the full game.
Maybe it's just having played the full version, but 150 bricks is extremely limiting.
Plus, I'd rather be able to play fully online, than have to just sit around playing by my self, with nothing more than a small amount of bricks and some Add-Ons.
IMO, the full game is worth the price, especially considering it's a one time payment, rather than the a monthly sort of thing. If ever you were to get the full version, which I recommend, you'd notice how boring the Demo version can be compared to the practically limitless, full version.