My comment: if you get on Wheel, and you're not happy with $25k, get over it, and regret you tried out for Wheel in the first place. Next time, try out for Millionaire, if you want some easy big money. You could've always sat in the audience for TPIR, where you'd have to get doubly lucky to (1) get on stage, (2) then win money by either playing one of the cash games and (3) winning big there or (4) getting lucky spinning their own big wheel, for $11k tops. When's the last time somebody's won $25k in cash on TPIR? *Thinks back* Not in my recent memory...
However, IN EFFORT to play along and try to fix something that doesn't require such, I offer this for WOF. You solve the puzzle, Pat opens the card, and he reveals $25k. NOW, Pat says, "Great, you can walk away with your $25k or if you want, you can come back tomorrow and try to improve on that, and possibly win $100k in the bonus then..."
However, by coming back, you risk everything you've won for the first day. Now we'd really see who'd bit** about winning $25k. You could even throw in some extra big money cards the next day for players who wanna be risky, giving them more of a incentive.
Another solution? Bring back the returning champs format. People should be ecstatic they'll be back again anyway, I'd believe, so maybe the whiners will be happy enough their "dissatisfaction with $25k" won't show. Nevertheless, returning champs always sounds like a good idea for Wheel to have again...
However, I wouldn't change a thing about that bonus round at this point, if I had my druthers. There's no need.