We use the Disney Dollars in my house as well. If anyone ask what to get my children for Christmas, Birthdays , etc. I always say Disney Dollars. I hold on to them until the trip. My girls can earn extra dollars or lose dollars(I always give them an opportunity to earn them back) based on behavior.
Our Disney routine is to go to Downtown Disney soon after arriving. We let the kids pick out a few things we will need right away such as autograph books, pins to trade, and a new shirt. We then scope out what they really want. We continue to only
look the rest of the week unless I know it is an item that can only be purchased at that particular spot. At the end of the week, and after they have changed their minds several times, we return to spend their Disney dollars. We have found this works very well for us. We don't have to worry about buyer's remorse or running out of spending money the first day of the trip.
In my opinion, one of the best souvenirs for little girls are the special My Little Ponies and accessories and/or Mr. Potato Head and parts. They are unique but Disney themed and will continue to be played with long after the trip is over.