Very true about the diminishing difference in value with age - that curve can be pretty steep, at some point you're not exactly hurting anything by doing what you please with it.
Didactically, there are differing views of audio nirvana, and no single one is correct for everyone. The capitalists you are so satisfied to have eluded may not represent the same specter to others. I find it hard to will away the differences between cables because I don't want them to be there out of financial self-interest (or for some, an intellectual desire to debunk the idea that there are performance differences.)
I live by the rule that what I purchase should be in line with what I am willing to spend for the improvement in sound it brings. If it underachieves, I get rid of it. If it overachieves, I consider it a bargain on my personal scale. To some, bare copper wire at a few cents a foot and its performance profile define this price/performance ratio. For others, it may be a $200/m pair of interconnects made by a hi-fi brand. For some, $1000 or more a meter seems a fair price. It's all in what you hear, and what you're comfortable spending.
To say that one hears the difference between cables because they want to seems equivalent to saying one doesn't hear the difference because they don't want to. Is it all psychological then? There are electrical differences that are measurable, why would there not be performance differences? I think that one's been discussed a few times before, as well : )