It would be great (and it would makes sense, in my opinion) if the player character could be granted some powerful, unique vampire spells upon becoming a vampire, which become even stronger as the level of vampirism (or perhaps the character level) goes up. I had them added to the game through the console, recently (something like "Fearsome Blood Theft" or "Call Companion") and found them not so unbalancing, considering the increased level of difficulty OOO poses. Sure, you would gain early access to the paralyze effect for spellmaking, but that's not really of use, unless your character has a high starting value for Illusion.
Regarding "Call Companion" or similar vampire summmons, I made an unpleasant discovery: the creatures (golems or shadow wolves) tend to turn against the player, and that's a real shame
It must be something in the script, or a matter of factions?
As a side note: the fancy vampire spells should disappear from the spellbook once you're cured of vampirism.
I know, this is more easily said than done. I would be glad to hear your opinions.