I'm wallpaper-obsessed and I recommend Kuvva (http://www.kuvva.com ). It gives you curates bursts of 7+ quality original wallpapers every week, on iOS and OSX, thanks to a partnership with actual art galleries.

This said, I think there's still a niche for a website or app specialising in new minimalistic wallpapers. Also, I'd pay for a "wallpaper-on-demand" service where one could order custom pics - I think photo websites like 500px are missing a trick there.