I wouldn't do the island. It's a waste of potential water storage, and will contribute to sedimentation.
Good point on the sedimentation. Also taking up water storage was something I thought of. But if I add a high output well, I thought perhaps I wouldn't need the additional water.
As for sedimentation, would enough rock along the island shoreline combate that?
Some "pros" that have me leaning toward it are
1) fun camping site
2) additional structure and elevation change for fish instead of just wide open water
3) potential duck nesting site
4) potential area to set up a duck/goose blind
