Have you seen the The Free Universal Construction Kit? It's a super-clever set of connectors that allow you to combine different types of toys. Like hook up your Lego to Fischertechnik. Needless to say, kids love it!
All of the weekly contests have been great! I think it's more of a intensive issue as far as participation goes.
If I were a part of Shapeways' upper management I'd give the community managers an allotment of 10 to 25 thousand dollars per year to offer up as prizes. I'd then have that increase to around 500 thousand in later years. The reason is, in the future, whomever obtains the loyalty of the masses when it comes to the designer types, they will be most successful overall. A company who falls behind in this regard could never compete by hiring designers to generate new designs. They could never compete with crowd sourced designs.
Currently, the playing field is fairly even in my opinion. Shapeways nor any of the competitors that have sprung up haven't really begun tapping into the multi billion dollar consumer market. Yet, as things continue to progress, I think that more and more it will be of the utmost importance to get the masses of designers on your side.