QuietArts, I understand your concerns but respawning enemy's is not the answer, I got a better idea for places that have already been explored (little fun quests like monster hunter, bounty, treasure hunting and so on)
Read this:
http://larian.uservoice.com/forums/...dynamic-and-engaging-gameplay-system-ple - Go find this part "Now lets talks about more ADDICTIVE activities to do in the game"
You also made me another idea, side events can be occurred during your paths if you need to visit the area again. Example a imp on the road that was not there before when you need to travel to the same area. I'm sure these little small events can make travelling allot more fun as well

Oh by the way there will be an arena in game, so I am sure you'll have allot of fun on that too

Hope you leave a comment and vote as this does satisfy most people who want to do more combat and other things to do in the game.
So QuietArts I do agree that there was nothing to interact with when your done exploring the area on D:OS or nothing really happening when travelling to the same destination as you already looted and interacted with everything, just respawning enemy's is not really the answer as it does get repetitive and annoying :P