I can sort of see the point about wanting to play an ice-mage in an ice-campaign, but such a specific campaign should come up with its own rules on energy types anyway. I don't see why vanilla D&D should have to incorporate all those permutations.
The idea of strengthening monsters through your attacks is horrible. Your entire party will hate you for giving the dragon its breathweapon back, making it an even stronger deterrent. Under the current system you can just throw your daily at the dragon and accept you'll do 10 points of damage less. At least that makes you inefficient, not suicidal.
The idea that a fire elemental can walk through magma but is hurt if you poke it three times with a torch is also fascinatingly bizarre.
That said, some of these ideas are still cool and can be recycled somewhere. Most frost knights should just crumble away a bit from icy blasts, but I can totally see a special version that recharges an encounter power or draws strength from it.
Such monsters would have to come with a special warning though. Depending on the party makeup they are either highly lethal, or half their powers are meaningless. A kind of design 4e so far doesn't want to promote, beyond undead and radiant/necrotic.