As you see: well thought!
Woman: nothing too short and open for views!
Jeans: O.K.!
Man: nothing too short and open for views!
You must not be dressed like you are going on a funaral or wedding. But a certain kind of respect should be shown.
Especially when you walk into the basements to see the gravestone of John Paul II. - everybody is well dressed there, and pray for him. And if you want to feel comfortable you should wear something which fits.
It's a place of faith, silence and respect.
Regards,
HeinBloed (just back from Rome)