Ha, you worry about the sunroof being open? How about the entire top! I did have a bird poo in my car once with the top down, but it has leather seats so it easily wipes away. Maybe if they were cloth I'd be more worried.

I seldom leave anything of importance in my car anyway, and if I do I lock the doors. I don't think joyriders even exist here, so I'm not worried about it getting stolen either.