Well, for me, and I know my answer might be weird, I plan to buy it at release... As I planned to buy every AI War extensions at release... But I still bought them during the betas ;-) So, playing with words here : I plan, but if I feel like I will play it, I might change the moment I will buy it actually...
For the moment, I'm quite mixed due to certain reasons... I don't like much the graphics, but hey, that's not a critic, that's just my own tastes... I had the same problem with AI War until... well... until I played it ;-)
I'm almost sure it will be the same with AVWW... I will for sure download the demo first, and there, have a game... When I shut it down, if 20 minutes elapsed, well, I should play more to be sure I won't miss something... If hours have elapsed, well, I buy it straight away :p
Plus, you have one really good argument for me : you're running on the Mac OS X natively (hate multi-boot), and only this could make me buying it !
(yet another comment full of unuseful information ;-) )