For those that claim this in no way will upset the balance of DDO, just have a quick look at how well the AC-system is working as of right now. This demonstrates the shortcomning of the d20-system, and if that basic mechanism is not about to change then further steps down the slope of power creep should be avoided for the good of the game.
This is under the basic but very likely assumption that if people buy +3 tomes now, they're gonna be back in the stores and higher level rewards will need to be implemented in game to encourage actual playing.