ever had a parts

ever tried to improve the internals of a device and have it backfire? For example, the caps in my tube phono pre were professionally upgraded, and yes, it is clear and fast and dynamic - but now I just about jump out of the chair on a skip or scratch, and sibilance on some vocals seems to have increased. Now I am thinking twice about "upgrading" caps in the power amp. There seem to be two schools of thought, and one camp seems to think better parts are almost always a good idea, and another, that the "voicing" the designer achieved will be disrupted by any change, not necessarily for the better.
I once added additional filtering capacitance to a regulated power supply, and it became an oscillator!!
Lloydc, you are so right.If it was that easy, all you have to do is pick the most expensive parts and you will get a winner.