I like it as it is. When every solid hit at mid-level or higher play invokes a MD save, that's when the Law of Averages comes into play and the inevitable roll of a natural 1 on that d20 appears. Go on and smack them then for 10-25 points of damage at a go; after making 5-10 MD saves in a single round, they'll blow a roll and then the PCs go down.
Force saving throws whenever you can. The increase in random rolls is an increase in overall randomness, and--as pointed out in the DMG--this always works against the PCs.