Hey Tiffer,
I received my $500 gift card a few weeks back - I still stare at it and think of all the blood, sweat, and tears (ok, clicks) that went into getting it. No doubt those that are closing in on it (Icon, Yoban, Infinito, probably a few others I'm forgetting) are having a bittersweet experience as well.
So is all the work worth $500 bucks? Heck no :-), but when you add the personal enjoyment factor of playing this game so frequently for free (you, myself, and many others have been able to play from a 'credit positive' position for quite a while now, not spending any of our own hard earned real coin), I think the price gets closer to being right.
Bogey's right, the poor prize/credit conversion rate is WGT's price for their cost of investment, maintenance, and enhancements for the site we all waste so many hours a day playing! Happy hitting and enjoy the chase to the gift card before it starts to torture you like it did me!