People who own the really expensive stuff and still find it lacking assuming its well set up look to whatever else they can at that point to make further tweaks. Wires are a prime candidate. The logic is you have expensive stuff and don’t want to skimp on the wires. Wires can make a noticeable difference in the sound in many cases, like seasoning in soup, but not always and cost may or may not be the reason.
For most people I would recommend get the major components and their integration into the room right first and cost is NOT the primary factor for that. Bigger rooms will cost more in general, that’s the only rule. Mogami wires are always a perfect choice. So are most any commercial grade balanced interconnects if an option. If you must play around from there, so be it. If that involves throwing more money at the wires, more power to you. To each his own.