I have the necromage perk, 100 skill in enchanting, and the insightful enchanter perk. I just had Serana turn me into a vampire lord with the expectation that I would get a 25% boost to my enchantments. But when I made a fortify smithing ring, it was still only a 25% improvement (with a grand soul gem), the same as if I did not have necromage and was not a vampire. Does vampire lord work the same as generic vampire for enchanting purposes? Does necromage apply to skill enchantments?

Are you trying to do the Alchemy Enchanting Loop?
You should find a guide for that, YouTube has a video.

The Necromage perk applies to you. Equip your Fortify Smithing 25% ring and then look in your active effects. The effect applied to you will be higher (31%). If you have an improved item which was improved as high as you could before you were a Vampire, then attempt to improve it after becoming a Necromage Vampire (wearing your Fortify Smithing gear) you will see just how much more you can add to it.

If you use the Enchanting/Alchemy loop as a Necromage Vampire, I believe you can get an improvement of 33-40% on each item (when it's equipped), which for me is too overpowered.

The fortify enchanting potion is pretty weak, at maximum strength that is alchemy 100, all relevant perks and five pieces of +25% alchemy gear you can make fortify enchant 34% potions.
However as the potion only boost the skill part and not the perks the effect is less than 20%. Enables you to go from +25% skill gear to +29% who again let you make +37% potions.
Worth doing if you already have maxed the crafting skill but not an goal in it self.
Will the necromage ability also boost potions? this would change things a bit as you both get an boost from the enchants then making the potion and the potion then drinking it.

This would probably have an huge impact on the smithing potion, enables you to make some ridiculous powerful weapons.

Thanks for the info. I was expecting the effect to show up on the ring, not in my active effects.

What this means is that my previous +25% apparel would be just as effective, no need to make new apparel after becoming a vampire.

BTW, I have sworn off all fortify enchanting potions. This is my informal method of limiting just how OP I can get. But I was willing to make an exception for smithing Auriel's bow since I wanted that to be my primary weapon.

The Necromage perk for Vampires adds to almost everything where a magical effect is applied. With enchanted gear made with the Necromage perk I can make a Fortify Smithing potion of 184%. I made a huge mistake after I became a Necromage Vampire of going and improving my weapons without thinking. I ended up making my Ebony Bow do 708 damage, and by the time I realised the insanity, I no longer had a save to revert to (my weapons are special to me, and I won't replace them). I ended up having to use the console to remove some Archery perks, so that I could keep using it.