One other suggestion is, like the banners for the website, to give the users a chance to showcase what they would like the site to look like.
Some websites, where there aren't many programmers/designers, may only require a free-hand drawing of the desired style. (Trust me, it is easier to have a drawing that doing everything by yourself.)
Other websites, with designers and/or programmers, may show their ideas.
The winning idea would be the one that is implemented, and with an award. Some merchandise would be a do-able idea. It saves you money, time and non-material resourses.
This is a win-win situation. I can't see how StackExchange would lose with this. And everybody has the look they like and want on their website.
