Have you thought about a time-limited demo (10 mins or so) but allowing import of models? Reason being perhaps someone who does modelling would just like to check it out quickly to see whats possible to import, how it works, etc.? They created a model for another sim and would like to know if it can be importet into outerra. Yes I know if its cheap and they do modelling they will likely buy it, but any roadblock out of there way should be encouraged IMO.
If you want to release it in a similar fashion to minecraft (great game btw), I really do think you need to release early and often, finished/polished or not. I have doubts it would work by simple releasing something when its "done". Another game dev that does something similar is
wolfire for their overgrowth game. They do weekly dev video updates, and anyone who preordered the game can play up to date alphas. Their game too is more of a tech-demo right now.