It's not really comparable though? The revisions would probably have pretty minor changes, while a new magic set basically gives you a new game. Drafts are really fun to play too, but again, it's just not comparable in my opinion.Most Magic players spend well over $50 per set. A few drafts will run that. It's not unusual for many players in our store to buy a box of each set (36 packs, about $120 locally). Some (like me) buy cases! (6 boxes)
Btw, try out Dominion if you haven't already.

Personally, I think that if errata/small changes just went to the pdf's/digital tools, and newer printing of the books, it would be fine. Even if I tried playing non-errataed 4e in a fully updated 4e game, it wouldn't really create much problems.