It's true that we can limit ourselves to what we can afford. It's not practical to upgrade if the amp/speakers has a good sound already. But the problem arise when we hear high end amps or speakers, realizing that it has better components which result to better sound quality. That realization is a growth to our audio experience. We can't ignore the fact that those cap upgrades, crossover modifications can really result to audio nirvana. Because, if this upgrade or modification things were not true, Do It Yourself guys may not exist after all. For me I became a D.I.Y guy "wannabe," to satisfy myself and be able to imitate at least some good SQ of those high end audio components I heard/tested. I can't afford those high end audio gears. Thus, I would say that modification is really fun esp.if it is successful.
So those guys who can afford and have the guts to modify your gears, keep it up. But don't forget to seek technical assistance from the experts, if we are not experienced to do it.
"Learning is a never ending process." Only a fool will say he already knows everything.