I used some of my 'wishes' for spa treatments during out trip in October. Great use of a 'wish'!!!
I don't know if it varies by spa location as to what is a 'wish' treatment but I called the Spa at the Grand Floridian and told them I wanted to use some 'wishes'- they had few different treatments that they allow 'wishes' to be used for. I had a 30 minute facial and a body salt scrub with two wishes (I think). A massage was also another 'wish' treatment'.
I booked about a month before the date and just told them at the booking time that I would be using 'wishes'. They had it noted when I arrived so all I had to do was present my room key to deduct the 'wishes'. Pretty easy!