It's a great idea in theory... and one that really should be amicable. Still, I think about paying five bucks for what's usually considered a free resource to the community and beyond, and I'm thinking: "These better be some DAMN good wallpapers..."
Of course yours are, but people are cheap. We cater to l33ch3rs... it's part of are rep as wallpaper activists and how we do so well. it's totally non-discriminatory. Charging sort of changes that----and i think in the long run, you'll end up just being pissed off becuase it's only going to take one five-dollar bill in your pocket to put your work up on a Warez site and everyone starts getting it for free anyway.
If it were me, I wouldn't even consider it. It's just adding another potential headache or future disappointment.