My fiance is from Miami, and I've been several times.
You don't have to spend tons of money to have a good time.
The beaches aren't that expensive, and while you can blow a lot of $$ at clubs, I don't think it's as bad as everyone's saying. That's just me, though.
You DO need a car to get around. There are buses and the Metrorail, but buses get busy and the Metrorail hardly goes anywhere.
Stuff you don't want to miss:
- South Beach - even if you only go people-watching, it's a blast. Plus, the Art Deco architecture is too cool to miss.
- Lincoln Road - shopping, shopping, shopping!
If you can, do an Everglades tour. It's beautiful out there, and no, you won't get eaten by an alligator. :P
Yes, a lot of people are Cuban (my fiance is Cuban-American), but no, Spanish isn't required. I do suggest you try Cuban food, though. It's super-yum.
Versailles over on Calle Ocho (SW 8th Street) is probably your best bet, but Havana Miami on Miller Drive is great, too.