What to do with a spare Vlad?

Level up the np unless you have np5 never burn a 5 star since you can burn trash tier 4 stars like stheno and fion for mana prisms.

Damage gain from first NP level up is highest (33% for most servants) so effects are very noticeable. Anyways, 5 star servants are quite rare so burning them is't a very good idea.

Never burn a 5* unless it already reached NP 5 since 5*s are rare and generally always worth the investment.

If you're desperate for MP or RP, burn 4*s or 3* servants/CEs, although 30 AP ember dailies are best for MP farming.

Getting Vlad NP2 will increase his damage output by 33%.

Furthermore, you can overchage his NP bar but since his NP gain is poor, it is mainly used to prevent some mobs like Ghosts from draining your NP bar below 100% and preveting you from launching Vlad's NP next turn.

So the increase in his damage output and to be able to overchage is two differents things.

Rare prisms will be valuable if you are a recent/new player as you can unlock with them the old stuff like the mystic codes (Battle Suit, Mage's Association...) and the two first Da Vinci's CE (Mona Lisa and Personal Training). If you are an old player and you have all of these, it is not worth it.