As a Vampire Lord you gain access to a skill tree with some perks in it. What happens to points spent in these perks if you are cured? Are they refunded to be spent elsewhere or are they used up permanently?
Once Vampire Lord/Werewolf perk points are used, they're set permanently. If you cure yourself and then get re-infected you'll retain all of the perks you originally unlocked. As the wikia article describes it:
Perk points allocated to the tree cannot be undone, although the vampirism can be cured through Falion's ritual. Requiring a filled Black Soul Gem, the affliction is reversed but all perks remain.
Also, it's not immediately clear what you mean by "to be spent elsewhere", but perk points for VL/Werewolf are drawn from their own pools. You can't spend them on the normal perk trees or on each other's trees.