Wow, seems like you have a packed day already- did my 30th bday there (over several days) - one day was driving 4x4 quads in the desert, one night a dinner-theater show, one night at the
dueling piano bar in NY NY, and some other things.
The Hoover Dam is probably one of the cheapest things you can do if you find the time, get a car rental for the day and drive down... about a 45 min drive each way.