I'm not an expert, but I've dove the Keys and Boca, and there isn't a lot in the keys that you can't see off of Boca (Hillsboro and whatnot). The biggest thing is just knowing where to go.
That being said, even if there is a lot more (which there are in some spots, there aren't in some spots) the reefs in the Keys (at least the larger ones with more activity in them) are offshore by a mile or more in the outer reefs.
I'm still interested to see if anyone has any good spots near the highway. If it's close enough, I imagine you could probably just snorkel out to them.
