The way I see it, this is a good mechanic to get new members to the site AND make them active as well. Knowing there is this kind of contest, the new guys are more inclined to upload here a lot more models than they normally would and this is good for the entire site because more models means there's a greater diversity of products available thus more possible clients will arrive on the site based on their keyword searches throughout google or other search engines.
So even thou this means you may never get to win this challenge, if you look at the bigger picture, this contest might actually help you by drawing in more visitors on the site and thus possible clients for your products and everyone else's.
I believe this is a win-win situation either way.