To be perfectly honest, I never encountered any drunks or derelicts in the keys, but I'm confident there must be some at every anchorage, especially the more congested ones.
The Garrison Bight Mooring Field looked like it was filled to capacity the last time I went through there, and I opted to anchor up in Mule Key Basin, which is just on the west side of the Northwest Channel. There wasn't anyone there other than myself.
Now, I spent most of my time in Marathon Key's Boot Key Harbor, about a month on a mooring ball and three months tied to the City Marina bulkhead. Never had any problems with the folks there either. Well, I forgot about a nutcase drunken woman who lived aboard a trawler on the other side of the canal who went berserk one night while we were playing music at the marina's Tiki hut. She was sent packing by the marina a week later.
By and large, pretty much everyone I met while cruising have been wonderful individuals. Now, at some anchorages in Chesapeake Bay, which is where I'm at now, there have been some pretty rowdy individuals playing loud music until 3 am and the Natural Resources Police had to intervene. I understand that most of those problems have been taken care of during the past two years of law enforcement.
Good luck on your retirement, and I sincerely believe you will enjoy a memorable and enjoyable time in Key West and the other Florida Keys locations.