As far as the cleric having many ways to get rid of undead, yes there are some, but nothing as overt as Holy Bolt (a 1st level spell). Turn undead is nice but will probably just take care of some skellies and zombies...not vampires.
As far as who unholy bolt would affect? Well as I said its all pretty arbitrary, maybe good creatures and dragons. Undead do get special immunities and things but they have no con bonus. Inherently that gives them many advantages, but it also means they have few hp. Your spell doesnt hold them or make you invisible to them or even command or rebuke them, it just kills them.
I think 1d8+1 is balanced mechanically, but I think its a dangerous flavor to have.
Technik
As far as who unholy bolt would affect? Well as I said its all pretty arbitrary, maybe good creatures and dragons. Undead do get special immunities and things but they have no con bonus. Inherently that gives them many advantages, but it also means they have few hp. Your spell doesnt hold them or make you invisible to them or even command or rebuke them, it just kills them.
I think 1d8+1 is balanced mechanically, but I think its a dangerous flavor to have.
Technik