Hm, I sort of preferred the elemental temple thing, but anyway! A few suggestions:
A.)Customisable spaceships? I mean, so you can mix'n'match however you like, though that might be a bit off the main concept.
B.)Shops. What big airport doesn't have shops?
C.)Lots of conveyor belts.
D.)Something unique for a background. Personally I think that there must be something better than just stars and planets in a space tileset. Not sure what, but something that looks good.
E.)Toilets. What big airport doesn't have toilets?

I'll probably think of something better later.