The JW in Brickell is definitely a well-run hotel.

Last time I was there, I received a hand written note from the GM thanking me for staying at the hotel and providing me with his cell number in case I had any issues. I don't recall getting much of an upgrade, however, but didn't really ask since it was a quick trip. The note was a really nice touch though, considering I only stay at this hotel every couple of years or so.

A lot of this depends on the occupancy, whether someone has booked the suites for a wedding/party, and whether there are PP's or Plats at the hotel.

If you show your loyalty to Marriott, and get to a higher elite status, they generally appreciate it.