The rule of doubling is my rule of thumb. Noticeable differences occur when you DOUBLE the list price of a component. Since this is a geometrical progression most people reach a plateau very quickly! Please note that this is a VERY crude scale, and has much less of an application for speakers and cables.
Law of Diminishing Returns; where does it kick in?
I think that most of us who have been in this hobby for a while have experienced the "law of diminishing returns", the point at which spending a lot more money produces a little bit better sound or just tradeoffs.
I would like your opinions on where you believe this occurs in Speakers, Amps, CD players, and cabling.