Increasing the mob HP and Difficulty isn't going to make the old dungeons fresh honestly lol Only newer dungeons with new bosses and mechanics and such are what make it new.

In the past they tried adding a harder difficulty for a dungeon, that was Pharos Sirius, and the community complained b/c it was too hard and every time it would pop up in DF people would drop b/c it required a good tank and healer.

Honestly, I don't think it was that bad but most the community thought otherwise. And this is what dungeons have become now.