I wrote an article a few years ago about my projects with crowdSPRING (which applies to other spec contests in general), which boiled down to clients acting as

I wrote an article a few years ago about my projects with crowdSPRING (which applies to other spec contests in general), which boiled down to clients acting as art directors. The people running the contests will ask for changes ("Oh, I'd rather have this over here"), which in a normal designer/client relationship, the designer has more power to say, "I wouldn't recommend doing that because of the UX/standards/good design/etc". However, with spec contests, designers will keep making the changes that the client wants because that's how they'd win the contest. Your home page isn't just about what looks pretty. It's also going to be how well things work/how to drive your customers to converting. And spec contests reduce it down to just prettiness. I'd recommend working with a freelancer or a design firm, who will do more than just placing a skin on your site but also keeps conversion in mind as well.