Here is my plan:

1. Get Vampirism to get Necromage boost
2. Wear full set of smithing enhancing gear (with Necromage boost)
3. Improve my weapons and armors (with Necromage boost)

My question is this; if I enchange my gear with the necromage boost, and cure myself of Vampirism, will the gear still benefit from enhanced armor and damage boosts?

The necromage perk would enhance your smithing gear by 25% once that gear is made it doesn't not matter who uses it. Your weapons and armor don't suddenly get weaker because you removed the fortify smithing items.

Yeah, just wanted to make sure I didn't get stymied by some rogue bug or something. Thanks for the info!