EVERYBODY. CAN. DO. IT. ALREADY.
So, if that's the only benefit of the PrC, it *is* worthless. However, you're likely misremembering what ability, exactly, the BoVD PrC granted. It probably did something like change your spell's sneak attack damage into Vile damage or something similar.
Furthermore, have you ever read the Exotic Weapon Master PrC?
He gets a really cool special ability that lets him treat a one-handed exotic weapon, when wielded in two-hands, as a two-handed weapon for purposes of Power Attack.
I leave the relevance of this data point as an exercise to the reader.
Absolutely - and that's the way the rule works, currently. In other words, it works exactly the same for a spell as it does with a crossbow.