it's not all the putter, but a good putter that you feel comfortable with and responds predictably can be worth an awful lot. I build golf clubs as a hobby, my first attempt resulted in a bad putter and I could never get a feel for it. My second attempt has been in my bag for the last 10 years and I don't see it going anywhere soon. It has the weight and length I was looking for and I am far more consistent with it. That said, it's hard to say what that's worth, but I'd guess it saves me at least a stroke per round.
I see what you are getting at, though. Often times, when I played consistently, I'd golf with someone who claimed things like "I could drive the ball 300 yards if I had that driver, too!". It would usually prompt me to yank their driver out of their bag and hit it as well as mine and toss it back to them.