I have assembled a decent system and looking to make cable upgrades.
I would never put that amount of money into any kind of cable.
You don't need to go fancy (or expensive) to get the highest sound quality, as long as you have the right cables. For speaker cables the gauge is obviously very important. For long cable runs, especially with mics or guitars at the end, balanced cables are the way to go to reduce interferences.
Some headphone cables are overly thin, so again a question of the right gauge.
Switching to different materials, like silver, doesn't help. I've talked to some mastering engineers and they neither use expensive audiophile nor the cheapest cables they can find, but solid, durable, reasonably priced cables (you'd say they're cheap compared to what some audiophile cables cost).