When people see that a game maker program is in flux, they always wait for the next version to come out before they try to learn to use it. You did very well on steam. Many people seemed interested. Then you lost your main programmer and now you are starting all over again. I think that was a big turn off for people.
As for modeling contests. I think that all the entries for the contest should be made free to use for all people. That way you can grow a large library of free content. That really attracts users
A nice clean page featuring all of the free content would be nice. A picture of the model, The poly count, The creator. A page that is clean and easy to search through.That's my 2 cents for now