The way I visualize cables is that it's not an all or nothing thing. It's a bit like a game of telephone. With lower performing cables being like a bad telephone game player. Once you lose some of the message you aren't going to get it back. The more bad players you replace with good players, the more of the message you're going to get at the end. It's just the same as replacing faulty wiring in your amplifier, which I had to do because the secondhand Beta22 amp I had was sucky internally and was cobbled together from random parts - or improving any part of your stereo. The bad player isn't really going to make a substantial change to the message - like making up something completely new and replacing the message entirely, but a few of the words get changed around perhaps. The hard part is figuring out when you've really produced an improvement. As you experiment you'll figure out which cables are the best value to replace.
This same philosophy is what leads me to be amused when people say that if recording studios don't use the very best cables then why should anyone use fancier cables than theirs. However, the recording that we buy is as good as it's going to get. The goal is to reproduce it, not somehow better the studio with our own gear...but to get as close to the recording as possible, even though perhaps the original recording could become better if it were recorded on nicer gear, or with nicer cables, or improving whatever parameters. Improving any part of your stereo gets rid of bad telephone game players and you get closer to the untainted original recording, and often there's more on the recording that one things, which is why when you buy a fresh pair of HD800s or LCD3s you get a new sense of how your recordings "really" sound or at least it feels that way as new details emerge.
Disclaimer: I'm not trying to advocate spending a fortune on cables. Because everyone hears things differently, some are true believers and some are not. Often the psychological boost of a cable is as important as any physical gains, if not more so. Some stereos and some headphones are cable sensitive, others are less sensitive. As an example, HD800s are easier to notice different cables on than LCD2s which are not picky at all. Some of the best cables out there are ones built from humble parts.