We took my "almost five" year old niece in September. Based on the advice from the Disboards, I booked the hair only package. She already had a Cinderella dress and wore it to the "appointment." I also purchased glittery pink nail polish at home and did her nails just before we caught the bus to DD ($2.50 a bottle rather than $10). I watched the Fairy Godmother very closely and was able to replicate the princess hairstyle for my niece's bithday party a few weeks later!
She absolutely loved it and I thought for $35 it was well worth it.
Another "hint" - After we got home I saw that our local Target sold hair extensions for girls that were almost the same as the Disney ones. For $6, I bought a long, dark brown curly "Belle" style. My niece dressed up as Belle for Halloween and looked just beautiful!
Donna