True, 4 cc is quite high cost to pay in early and midgame. However in late-game itís easily doable and gives undue advantage of unlimited stealing, as well as discount casting cost (cc) on stolen stuff. That discount acts as unduely oppressive advantage of kind-of resource ramp in situation when opponent is already hurting - loosing his cards while Rouge is gaining his, therefore hugely gaining one of biggest advantages in this game which is card advantage, milling deck, gaining access to more play options due to another card pool while opponent is loosing his options, maybe even win conditions (like some Fireballs to be able to do enough dmg to close match, etc.)

Having thought about it for long time I think it should finally be balanced like this:

Still 2cc to cast and 4cc to make a steal, but loose all the discounting of casting costs for all stolen stuff and get a limit of 3 uses of durability. Cause unlimited use is too severly oppressive, especially when the match is in its late-game stage. Rogues, especially Serena, will still be strong if this change is made, so absolutely no worries there.