I asked exactly the same question afew days ago ... No replies so far.
I thought it logical that after sharing a Cubasis project to drop box we'd be able to import it back into another cubasis, but that doesn't work. I haven't tried iTunes File Sharing yet ... But that now in Involves another whole computer!
Could it be our loyal devs overlooked Cubasis. Being able to import its own projects? If so , add it to the feature requests please!
Cubase 7, Nuendo 6, Cubasis ( gotta luv it ), MR 816 cs, OS 10.8