still... my +5 mimicking frost scythe (a +7 weapon) gains flaming bust, keen and vorpral (a +9 - +10 weapon could get it) off my mate beside me when I charge... all of a sudden, I have an Epic scythe of doom... and a handy +2 bonus to attack!

This could really get abused by NPC's as well: imagine twin fighters, equal yet oposite in the sence one has a +2 mimicing flaming longsword and the other a +2 mimicing frost morning star. They teleport in, tap weapons (as they attack at each other, each parrying the others blow), and unleash the cold/burny/slashy/piercy/bludgeony magical attacks of furry that only a pair of flanking, re-occuing villans that teleport home when one of the reaches 1/3 hp can deal. Actually, make them blackguards... sneak attack. Or just an ettin that crosses weapons at the start of eack round (soaking up an attack from each arm each round, but hey... a pair of boots of speed negate that loss.)