That car rental rate game is the Holy Grail for me. Over time, I have saved hundreds of dollars, and made my relatives very happy, who previously thought "it is what it is." I will admit that I am obsessive about it - but it's a small vice.
I have a little chart that I print out to fill in so I can keep track of all of the codes, coupons, categories, etc. I subscribe to the email programs, I check Mousesavers, I read a number of boards to see what people are posting about new codes and their successes. I try not to fixate on the size of the car, or the return locations, if my other travel plans are not set in concrete.
I will make a new reservation to save $4. ...occasionally, I will spend more if I feel I am getting a better bang for the buck. (For instance, I found a covertible for a modest increase when my husband and I went on a special vacation last year. Although it cost me more money overall, I felt it was a much better value.)
To me it is a rush, when I see a price go down. I usually save all of my paperwork, from my first reservation when I start planning a trip months in advance, to my final plan....that's my secondary rush, when I find how much I saved from beginning to end. (Yea - I know - I need to get out more, don't I?)
Maddle