Am I right in thinking that once a die is placed on this card on a particular face that you can choose to spend this die for its face’s effect on future turns? If so, would the die go to the spent area for re-rolling on your next turn or does the talent allow you to choose to leave the die on the card for use on a future turn?
The effect of the Aether Reserve talent allows you to 'freeze' a die so that it is not rolled whenever you would roll your dice. This lets you keep a good roll for later. However, once the reserved die is spent, it comes off of the card and goes with your 'spent' dice. You can't keep a die on the card once it has been used. (You can put a different unused die on the card that same turn.)