Price is a factor in all this. At lower price levels, cables make a big difference. As component prices increase, spending more on cables hits the realm of diminishing returns before expenditure on electronics, speakers and vibration control does. And a good mains installation is more cost effective than spending money on more expensive cables. Last, absolutely correct speaker placement relative to walls, correct toe in and verticality is the cheapest upgrade of all if it hasn't been done in the first instance. All of that IMHO and experience.
What makes the biggest difference in sound quality?
When making changes or adding things to your system, what makes the bigger difference in sound quality on preamp‘s and power amps? Interconnects, speaker cables, power cords, or fuses?