I think you make a good point about the luck based contests. I like the other ones though. The ones that challenge people to create art, share recipes or write stories. This will just give people more reasons to create new, original content. The winners are mostly displayed in the announcement posts, so they get some extra publicity aswell. The photography contests really re-ignited my interest in that particular hobby of mine.
I might be a little biased though, because I run a contest where I ask people to write stories with words I provide. Not that I have more than two contestants most of the time. I'm no whale, so my contest's not interesting ;-)