I agree, Miami is a risky option for a refit as there are few DIY yards available and they take full advantage of that.
I have used Hurricane Cove on NW N river drive and they are really OK, with lots of DIY refits going on and good professionals close by if you get stuck, plus the additional benefit of having lots of marine suppliers close by, howver, they are having huge issues with polution and mainly because of this, insist on your boat being out of the water and you are restricted to working daylight hours with no liveaboard. The yard is VERY dirty and you will need to do some serious work on the topsides to bring it up to speed.
How serious of a refit are you needing? we found a great yard just by the junction of NW 22 Av bridge and NW N river drive, which offers the downtown miami experience, just at much better rates and a much cleaner smaller yard.
Once again though, I agree that for a small boat, you may well want to get out of Miami. I have a 44ft sailboat and she is based in Aventura, so this was a good option for me. You have the luxury of trailing your boat, so unless you have overwhelming reasons for being in Miami (we love it!) I would suggest you look for cheaper options else were.
There is the added bonus once you have completed work here, that you can enjoy the town and the sailing/fishing in Biscayne Bay and the sorrounding area (even the Intracoatal if your mast is less than 56ft) is really special. Once you have familiarised yourself with this area, your in the perfect spot for a reide across the stream to the Bahamas.