I have to take issue with your assumption that gamers must be "kicking themselves" for buying The Witcher in its original release. You delayed your gratification and will experience a presumably-improved Witcher as a result; I have already had the pleasure of the Witcher experience - and a great pleasure it was - but I'll still have the opportunity to taste its new sweetness when the enhanced edition is released. I think that's one of the great things about PC gaming: Enhanced releases like this (which are admittedly quite rare) are typically free for owners of the original game, something consoles have difficulty doing. Egosoft did the same thing with X3: Reunion, releasing a 2.0 version of the game that included the Bala Gi's Research Missions update, and also making that update available as a download for registered owners.
I want to say there's also some benefit, although perhaps a perverse benefit, to sampling a game as it was originally released, warts and all. Of course, that's easier to say when said warts can be disposed of through free updates; I might not be so magnanimous if I had to pay an extra 20 or 30 bucks to get the new Witcher release. But it comes back to the same point: As long as developers and publishers aren't ripping off their original user base by charging money for what are essentially "super-patches," there's no problem.
I guess it ultimately comes down to how strongly you feel about the game in question. I wanted X3: Reunion, but I also wanted to be sure it wasn't as deeply flawed as early reports portrayed it; I waited, and when I heard about the planned 2.0 release, I waited some more, and then when I saw it for a decent price I grabbed it. For The Witcher, on the other hand, I killed the two people who were standing in line in front of me so I could be first. If you start out with that particular mindset about a game, you're going to be far more apt to forgive a game's flaws when you bump into them.