Preservation is...fine? Here's a brief analysis:

Pros:

Has a Wild resource, which is useful for removing attachments, paying for Requirements, and managing card kickers (Tackle, Warlock, Second Wind, Protector, Nova, Black Widow)

Provides a benefit for 'free'

Healing is usually expensive and limited

Cons:

Limited to one per deck.

Fighting for limited slots in Protection.

Power of Protection is potentially better.

I understand the designer's intent in limiting this card to one per deck, but I think they were too conservative. Allowing two in a deck would make this card for more popular, allowing for some drip healing. Only allowing a single copy? Preservation will likely heal you two point of damage over an entire game, maybe three.

Preservation doesn't progress the game state in any meaningful way. It might counter a single Villain activation (assuming 3 damage) over the course of the game, but too slowly for you to notice. You have to compare that to another card that would take it's place. e.g. An Ally would likely absorb more than two points of damage, a Defense event that will block three damage at once.

So, there's nothing inherently wrong with Preservation, but I'm not sure if it measures up to the other resource-effect cards (Audacity, Determination, Innovation).

My rating is a C : Not a bad card in terms of efficiency, but most other cards have more value than this.