If you asked my three boys, YES... its worth it, but if you are going to do that, you might as well add on the water parks and more option to your park ticket for $50 and he can go there more than once. as for alone in the parks with a friend. yes... thats definately doable, depending on the maturity of your son. my kids all did that with each other. when my oldest was almost 17, I sent him off with his younger brothers, aged 14 and 10 and told them to keep together, the oldest had a cell phone at the time and then we had a set of walkie talkies . but the middle one did go off on his own and got back to the resort fine. so I wouldn't worry about it.
Last March we were down there with other family members... my then, 15 yr old several times acted as chaperone and tour guide for his two cousins... 14 and 13. My son had been there so many times, he knew his way around, they had never been there