When I'm working with a client that is really focusing on changing her spending habit, I do give her permission to spend a set amount to "treat" herself. This doesn't mean splurge on the latest Marc Jacobs handbag! I recently read a study that people are more apt to buy luxury items when they feel powerless (Journal of Consumer Research). This is so true! Think about how many times you went shopping and impulsively bought clothing or books or home goods that you didn't need. When you looked at our receipt later on, you probably couldn't believe that you spent so much!
It really is ok to treat yourself and buy yourself nice items or go out to dinner. Just make sure you spend a set amount. You will actually feel more powerful and confident - in your pocketbook - and everywhere else.