I think that if you really like the way your system sounds, you can try upgrading cables to bring out your system’s full potential, which expensive cables may or may not do. If you are not fully satisfied with your sound, I would go for new speakers or boxes until I got it to where I liked what I was hearing. As far as cables go, I found that speaker cables made the most dramatic difference.
How Important Are System Cable Upgrades and Where to Start?
My limited experience indicates that the order of most to least important is:
Room Treatment: Room selection/ Audio furniture (vinyl playback)/ Equipment placement /absorbers/diffusers
Component upgrade
Component power supply
Power Source conditioning &/or dedicated circuit
Power Cable
Interconnect
Speaker cable
The exact order of the first five items likely vary a good bit depending on the room, starting components and quality of power.
What are your priorities?
Are your priorities based upon trial and error, or the logic of your thinking?