Why no Clr/Rog PrC?

[Hypersmurf]

Enervation?

Deals additional sneak attack damage IIRC?

Yup.

And it's a spell that requires an attack roll, and deals damage.

Tome and Blood defined 'deals damage', for purpose of determining weaponlike spells, as hit point damage, ability damage, or negative levels.

-Hyp.