no they should only change thing that really need a change and leave thing that work fine alone and also they should implement completely new things no change the existing stuff and tell us it's completely new.
A positive example, inventing the phasing system and refining it was a great addiction to the game and something we all need to prise them, an example of a new tech created and implemented in way that rise the quality of the game.
A negative example, messing the stat system at the end of wrath was something uncalled for who was still hunting us even nowadays through blizzard try to fix it many time.