Surely thats just in the same way people try various amps and cd players aswell to "find the right sounding one"
You agree that one cable can sound different whether its technically accurate or not. People have their own preference of sound signatures so if someone can afford to spend this sort of money for something they want, why shouldn't they?
95% of cable companies simply buy cable in reels from China for peanuts and don't make their own from scratch - only a handful do - it's often a simple rebranding exercise, so the same reel type could be found on a £5/m cable and a £50/m one, just the latter 'looks nicer'. If my speaker wire was highly visible in a room, I'd pay more for looks, certainly yes.
True silly-money cable and other such things, there's no logical conclusion one extract from it other than it's a simple exercise in a few opportunists trying to get rich people to essentially give their money away to them. The fact that companies like Virtual Dynamics have gone kaput shows that at least some people with a lot of money realise this.
With a speaker company, they charge massive amounts for their flagship stuff because of the R&D that has gone into it, that it's all hand-made, the components and materials (I'm building some active speakers at the moment, and the cost of the electronics alone has been several hundred quid because they use high grade capacitors etc), there's a reason for it. They probably make a bit of a profit but they're not taking the ****, and the tech filters down the line into the cheaper stuff over time. If someone buys a £15,000 speaker cable, then I'd say the vast, vast majority of that money is just going straight into the owners pockets as they laugh all the way to the bank, because it doesn't cost much to make make a reel of wire look nicer. Put a new sleeve on it, talk about technical sounding stuff that doesn't apply to a cable's performance in an way (raising the inductance and resistance, or the capacitance does), call it SUPERMEGACABLE SERIES 3! Sell a few of them, that's your annual salary paid for. Release SUPERMEGACABLE SERIES 4 the next year, voila!
EDIT - in terms of system synergy... I'd rather go for as transparent and accurate/natural as possible (never 100% do-able), and then it's a case of what type of house-sound from xyz speaker company is the most preferable to my ears. If the speakers are bright, instead of going on an elaborate mission to tame them, I'd just get less bright speakers.