Also, I don't think a valuation of the entire game in necessary to calculate a value index of a single card.
IMO it's not possible to calculate a single value for each card as each card's value changes all the time.
The Value of Vampirism changes greatly depending on :
1- How many attack dice do you roll
2- How much life has the target left
3- is the opposing creature living or non living etc ...
A Spell like Force Hammer has a different value depending on whether the target is a conjuration or not ...
Not sure I agree 100% here. To me the only value a card can have is in terms of mana. AW has release Vampirism as a enchantment and had set a fixed value to the trait. So in this aspect the trait value is quite clear. And that goes for many other trait as well.
With that said, the effect of Vampirism will be very different depending on the current play state (not to be confused with value of the trait/card)
The value of a card just equals its mana cost? That is just not true. This is not fullmetal alchemist. There's no rule of equivalent exchange where the output resources (the stuff that gives it value) must always be equal to the input resources (actions/mana).
Case in point, meditation amulet costs 4 mana and a quick action to cast. After that each round you can choose to use a full action (the equivalent of two quick actions) to gain three mana. In terms of mana alone, it breaks even after only two uses. If you were only measuring it by mana, it would get more valuable over time. However, no matter how many times you use it, meditation amulet actually never breaks even in terms of actions and mana combined. It is a net loss of actions/mana over uses:
-4 mana-1 quick action
+3 mana-1 full aciton (~2 quick action)
=~(-1 mana-3 quick action)
+3 mana-1 full aciton (~2 quick action)
=~(2 mana -5 quick action)
+3 mana-1 full aciton (~2 quick action)
=5 mana -7quick action
So meditation amulet's total output never exceeds the total initial investment. You're losing actions faster than you're gaining mana. That's why meditation amulet is a lot more useful in builds with lots of creatures as opposed to solo builds. A net loss of your mage's action is less detrimental when you have multiple other creatures that can take actions (more than your opponent).
Does leather boots (cost 2 mana) have the same value as crown of protection (cost 2 mana)? It still varies, of course, but if you're a priestess, that uses creatures other than herself that don't already have more than 3 or 4 innate armor, then it very often does not have the same value. Crown of protection can increase armor by more than 1 over time, but only on non-mage creatures (whose survival often isn't as important as the mage's). Leather boots can increase armor by only 1, but can be used on the mage, and cannot be used on any non-mage creatures. Also, when do these two spells break even?
They both cost 2 mana and a quick action to cast. Then crown of protection costs 2 more mana and a quick action for each armor given. If we were talking purely in terms of total armor gained, crown of protection generally wins. If we're talking in terms of total net resources gained or lost, leather boots wins:
Leather Boots Crown of protection
-2 mana -1 quick action -2 mana-1 quick action
+1 armor +0 armor
-2 mana-1 quick action + 1 armor
=-4 mana -2 quick action+1 armor
-2 mana-1 quick action +1 armor
= -2 mana-1 quick action =-6 mana -3 quick action +2 armor
+1 armor
+1 armor
No, the value of a spell does not just equal it's mana cost. TBH I think a card's spellbook point cost is probably a MUCH closer approximation of that.