I'm in favor of adding hard modes to every dungeon with varying amounts of stones/rewards. That's essentially all you're asking for and slapping a solo-game label (New Game+) on it. However, we'd only find the most efficient dungeons for obtained loot and grind those, ignoring the rest same as we do now. You're not really adding anything new to the game. You're just repackaging what we've already got.

I do appreciate that this isn't another thread complaining about content though.