SlackerSupreme: The area I exploited was the never-ending spawns of Harpy's just outside the Visionary's home in Chapter 2. The respawn shut off either because I lifted the curse off Henselt, or maybe earlier when I walked through the mist, not sure. But the first time you encounter the guy, they never stop respawning, and they respawn like every 15 seconds.
They drop claws (which have no purpose I've found other than money), other harpy-based ingredients, and 1-2 lesser mutagens, which are the real money earners. I filled my packs and returned over and over, earned about 6K all told.
Yes! Another good one.
I don't think they give xp though. But that is besides the point.
Also, when I went there before having a quest to do so, I kept getting the Visionary's emote on my screen, no matter how far away I got.
Still, great cash crop.