Marcel Duchamp once said something to the effect that he didn't make art anymore because the world was already full of interesting things. Over the past year, I've seen new implications for this as far as concept design goes.
Sometimes common items have extraordinary shapes, and can serve as unexpected inspiration. The usual takeaway from Dada and Duchamp's readymades is that they're crude jests, but it seems to me that there are also lessons for designers in there as well. You can take everyday things and mix them together, cut holes in them, grossly change their scale, and get something new and interesting out of the affair. This helps prevent having spacecraft that look like flying dildos, even if you have to vandalize a public urinal to do it.
Spaceships are an odd case, because you want something unique and identifiable, while still maintaining a good feel of what it *does*. This is maybe even more true for designs for games, as being able to readily tell one type from another instantly is important for gameplay.