After 7 months of playing this thing came to my mind and made me sick!
The cards that say "spend 1 resource to do that" either from the very hero's pool (Glorfindel) or any other resource pool (Longbeard Map Maker-Lore)
do not limit that you pay one resource only yes? Can you not pay as many as you want to multiply the effect?
What about Radagast? Can you only heal 3 points of damage in a 3player game? I suppose you can heal less but you have in any case to pay X.