I have one of those Golden Age Passports too. Man, it is the BEST $10.00 investment I have ever made in my life [:D].
I can’t tell you how much money it has saved us because we love the NPs, monuments, etc. On the other hand, we usually feed the "donations" boxes that are appearing in many of the park’s visitor’s centers.
I NEVER regret any of my tax money (past or present) spent on National Parks.