Contest is a good idea but I have no time even for things that I am doing already. So I would put the level from my current project to a contest which includes only one course because as well my project is incomplete I basically just add some levels to a one collections. Making some separate sandbox levels would be so unreasonable because someones of us will decide to add their old sandbox level to a one game anyways.
I don't also don't have any designed title screens nor worlds as you know.
About the prize I think that you may push Ting_Thing with this because he even haven't got any considerable money for Platform Builder and he also agreed to give away PRO versions for free for them who will share his creation with the others. His Platform Builder have even no much popularity as you can see in this forum. Where he should get a money for the contests?
I think this thing should grow a bit before any contest for the money. Although for them who are using Standard he can give away PRO for free when they win the contest and if he wants to but I think we all or most of us are the PRO users.