My "theory" on changing putters has evolved......I used to use a putter until I had a couple of bad rounds with it, and then I would begin to find all kind of things wrong with it, so I could change. Then we started spending a month in Florida about 4 years ago. We are near Orlando, where they have an Edwin Watts, a PGA Super Store, and a couple of other golf stores. I came home with two new and fairly expensive putters in those 4 years. They met with a similar fate as every other putter I ever owned! The one has become my backup putter, and I just traded the other one in for a new golf bag at the store it came from (it pays to save receipts, BTW!).
What changed my mind about expensive putters was an experience I had back home last summer. I was in a Play It Again Sports on a "scouting trip," grabbed a bronze Rossie II out of a bag of old used putters, and this baby sat perfectly to my eye. It had a price tag of $15 on it....I offered them $10.....settled for $12! I have putted lights out with that putter ever since!! When I told my golfing buddy I had bought another putter, he gave me an eye roll, and I told him, "From now on, my only new putters will come from Play It Again Sports!!"