Instead of respawning monsters, I'd rather have random encounters a-la Fallout 1&2 where you can bump into interesting scenarios while you traverse the map.

So even if you cleared out a map of all enemies, there's a chance that you'll meet a random stranger needing rescue, clumsy bad guys getting caught plotting something, bandits, etc. Not that this game really needs any more XP. It's easy to become OP from low levels.

It's easy to make something difficult.
It's difficult to make something easy.