This is mostly in response to raze comment (it is minor and not totally relevant to this thread). I have in fact played games that have done resource management in a useful fashion (though I have to admit it is very difficult to achieve the following three (imho) required goals):

a) fun
b) good balance at start of the game
c) good balance at the end of the game (and one presume or hope in the middle).
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If the game has 'random' load out (and I think they should; read fun factor) then for certain resource management there can be a balancing act (if you find more at the start you might find less at the end; or if you have many resources you might find more of one kind but less of the other - such as component for fire or water spell).
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However that is not to say I think this is the right way for D:OS - it might (or might not) work for D:OS with regards to (a) being fun but would certainly require a bit of work. There can be a bit of procedural work that keeps track of a target total resource and as resources are randomly generated the global pool can decrease so it is certain do-able.
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The reason I'm not suggesting this is (or is not) the right approach for D:OS is because there are many different systems and I think they can all be fun and still balanced. I'm not sure I like the idea of a spell that takes many rounds to cast (certainly 1.5 rounds is ok but if it takes too long it creates other issues with game play mechanics). Having a long cool down is certainly a method to handle the balance factor but again I can see pro/cons.
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So why am I not advocating a definitive method (or my prefer method) because as I already said all methods can be fun and balanced (to a degree). If I had to pick a method I lean towards resources because I love treasure hunting and resources are a form of treasure but that's a petty reason to advocate a specific method for D:OS which has other forms of treasure hunting and need not extend spell casting to treasure hunting (after all they have equipment and crafting already).
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I will say that I tend to lean towards mana pool over cool down (esp if there are no 'mana' potions) but that doesn't mean one method is better than the other (I like mana pool because you can pick and choose how to break down your usage of the mana against a given set of spells with different cost - mana potions of course break this model because then there are less pro/con of high cost spells).
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Given that D:OS turn base mechanic is very much focus on action points one can argue with a lot of strength that casting time is very much consistent with D:OS model as well as cool down.
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Anyways I'm sure that whatever the final solution is some folks will be happy and others will complain and I myself will be satisfy for what it is as that will define the type of game that is D:OS (btw I really liked DKS (but the dragon part at the end was not my favorite part of the game) and I don't remember quite so many threads on how to warp DKS mechanics).