I'll totally buy into some scammy behavior like ship purchases. But that's basically the only source of cash until it actually ships (lol), and we all know that big engineering teams are very expensive.
I backed SC at the smallest level way back, and I still enjoy it from time to time. It's definitely very cool and unique, the progress is just slow. They're trying to do way too much, IMO, and they don't really know how to communicate timelines well with the community. Hell, I don't know how to create estimates well.
I think if the game had been in the hands of a talented game studio, things would have gone much differently. Having to build out the studio and company along with the game is likely a big task. Processes that already exist in a studio have to be created from scratch. Plus, a studio would have a much easier time cutting the scope to meet deadlines. :P
But I could totally be convinced that it's a real scam in the future. The amount of work that has been put into it so far seems quite large by my estimation, and I doubt they are just doing that work to run away with folks' cash. 300 engineers would cost enough that I could see them being tight on cash anyways, even with the large crowdfunding efforts.