I played Reunion - didn't make it to Mystic Dunes, but on a separate trip yesterday drove through Southern Dunes...
Reunion is generally terrific - currently playing nine Watson (Independance Course) and nine Palmer (Legacy Course). It gets little play - invitation only, and was in perfect condition. The Palmer nine is overdone, the mounding/sculpting looks artificial. Just too much. The Watson Course is very good. Good bunkering, naturalistic mounding, and closely mowed green surrounds giving many short game options. The last hole of the Watson course is wild - must be 30 bunkers, not sure... Looks like you play through a war zone. Ultimately Reunion will have 54 holes (18 each Palmer, Watson, and Nicklaus).
Southern Dunes looked nice, although the community doesn't look like much. I hope to play it on another trip - same goes for Mystic Dunes.
Steve