I agree with sgordon1. Smith's book didn't offer miracle advice but it did change my thinking about sound. I don't do many component changes (but sometimes, upgrades) and when I do, I first read everything I can find about it (and listen, if possible). Not just the glowing reviews. So the rate, for me, is probably closer to two out of three succesful.
New Component Upgrade Success Rate
I like to try a new component once in a while when the upgrade bug hits. Cables, tubes, power cords, power conditioners, headphones, maybe even something major like a preamp or a DAC. I've noticed my successful adoption rate is pretty low and I usually end up returning the new component. About one out of every four or five attempts is a success. I'm batting about .200. What is your successful adoption rate when you try something new?