Living here in Fl. The keys are not like they show on the TV or when I was a kid and teenager... On the drive down hotels, resorts, strip mall line the roads, the seven mile bridge is kinda cool. key West is really nothing but Duval street, lined with bars, t-shirt stores, tourist traps stores, more bars, and restaurants. There is only one beach that really sandy, Smathers B beach, I think that its the biggest one, open to the public, you will have to pay for parking. I think that there is a beach you can pay to access not sure of the cost somewhere in the 25 to 40 dollar per person range. The other beaches are a lot of crushed coral, shells and rocks mixed in with the sand. The beaches are not big area, and it does get crowded. If you venture off Duval... there are some nicer restaurants, do be careful, use you good judgement when out, drinking.
I will say that the sunset in the keys is absolutely just amazing. There is the celebration party... But for this Florida girl I like to watch it without all that.