I'll give you might opinion:
Just going on the cruise IS THE WOW FACTOR. The cruise, as you know, is non stop fun and excitement.
I agree with Donna that going to one of the specialty restaurants is a good idea for minimal money and a private dining adventure without much effort.
Save the money, don't bother with a balcony or fancy cabin. In fact, avoid hanging out in the cabins and be up and out and meet people. Participate in many of the events. READ the Compass (left in the stateroom each evening) throughout the entire day and highlight what interests you the most. You should typically find something specific to attend in the morning, afternoon and evening besides just food and the entertainment. For example, go to "The Love and Marriage Game" go to the Quest and PARTICIPATE (unless you find it offensive or objectionable. Go to the "cake decorating" or the napkin folding or the dance classes or Zumba, etc. Go to the Karyoke or any other events that you've typically never done before.
Enjoy the ports of call but DON"T MISS getting back on the ship by drinking too much or wondering around and losing track of time. The ship wait's for NOBODY except their own excursions.
Enjoy and it will be a very memorable birthday.