La Caretta rocks
I fly through Miami every year from SFO and my layovers START at 4 hours (I've had 6, I've had 10!). Its a pretty good hangout airport.
Here's a thought though - for $75 you can buy your way into the Admirals Club. That's what we did when we had a 6 hour layover a few years back and got in at the crack of dawn with little to no sleep. Free internet, snacks, coffee and soft drinks and a comfy place to be. I just got a credit card that one of the perks is access to airport lounges such as this so now I never fret a layover
What's a bit "sucky" about your situation is the travel time...but the fare is good so I guess you gotta suck it up - and you should, cause it's not that bad.