Do speaker cables really make a difference ?

Back in the days of yore everybody used lamp cord - and nobody complained!

Back in the days of yore, people played 78-rpm records on their Victrolas and nobody complained! I traded mine in for an 8-track for my Edsel! 😁

Yes

Depends on your system. This one likely can't be improved with speaker cables.  

In my humble opinion if the cables have sufficient insulation and are the correct Guage for the power you have and high conductive core. anything more is a waste of money!!

I did not read other posts, and this is the feedback from my own system. The cable differences in my system from most to least improvement is as follow: power cord for generator/conditioner; power cords for sources including streaming and disc transports; interconnects from DAC to pre, speaker cables, interconnects from pre to amps, and all others have small effects.