There is a very interesting article in the JRS by Mary Beard about the legal and sexual status of the vestal virgins. I will give references to it at a later date, because I can't remember off the top of my head.

Basically Beard looks back to the theory that the Vestal virgins were based on either the daughters or wives of the early Kings.

The clothes that they wear are symbolic of what women on their wedding day wedding day would wear. If you keep in mind this, then it explains their priviledges, they are released from manus of their guardian, because they are about to be married, but not yet under the control of their "husbands". The VV's were partly under control of the Pontifex, but even he was not allowed into the temple or quarters of the Vestals.

On being buried alive: the women who (supposibly) broke their vows of chasity, were buried alive, with only one days supply of food and water. It is important though to note that once they were buried in the chambers the ground was completely smoothed off and it was illegal to offer them any funeral libations. So not only were they killed, but cut off from the realm of the dead. A horrific punishment for a devout person.