I've tried the spas at various resorts including Aulani and on Disney Cruises and personally for the price I find I prefer the spa treatments I get at home.
I just had a Gel manicure at Senses at the Grand Floridian with Dana. It was more expensive than I get it for at home but she was very thorough and I was there for over 90 mins. It was very relaxing and I would definitely recommend it
"Worth it" is very subjective. If you enjoy spa treatments and can afford it, then go get you a spa treatment! It's your vacation, Disney or not, and you should do what will make you happy.