MOAR HITPOINTS MOAR DMGZ!!!
That makes for shitty difficulty improvements. I'd rather see something like the above. Various spellcasters throughout the land get access to a spell (or even consumable item?) called "Glitterdust" which they'll throw in the direction they suspect sneaking or invisible characters are.
Right now sneaking and invisibility are effectively "I WIN!" buttons.
Giving the baddies a means to combat this grossly unfair tactic (while still maintaining the tactics use in general) would improvve the game experience tremendously.