Can't have enough if you ask me. Now, I don't have EHD in my region, so there is that. My place is flat as a flapjack and seasonally wet. Anywhere I can dig a hole to hold water and use that excavated material to raise something else nearby, is a win win. I get water and a high spot to do something I otherwise couldn't do. What I do have is wolves, and I think spreading out water sources would make it a lot harder for wolves to hunt a choke point like a lone water source.
I've dug 4 of varying sizes and depths so far, and I'm shooting to do another 3-6 this year. Someday, I'd like to have them all big enough I can trap my own minnows in each to juice the forage base in my pond that doesn't exist yet.