My kids get Disney Dollars as gifts from my sister and their godparents. DD#2 (6 yo) had an expensive birthday party, so we only gave her $25. DD#1 (12 yo tomorrow!) was given the option of an expensive party or $75 and a couple of friends sleeping over....she chose the $75/sleepover option. It will play out that DD#1 has about $150 and DD#2 has about $100.
We did this with them last year and it worked very well. They knew that when it was gone, it was gone and we were not buying a single souvenir for them. They did great......DD#2 came home with $1 and DD#1 spent about half of hers on a nice pair of earrings (and we didn't have to cart home loads of plastic junk).