Do speaker cables really make a difference ?

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. 

Yes, they can make a significant difference. I had some custom made 1950’s 12 ga bi-wire NOS Western Electric cables on my Vandersteen 2CE Sigs, and when I got my Treo’s, a pair of AQ Comets were thrown into the deal. I didn’t initially use them, as I thought my NOS Western Electric were very nice, (and indeed, they are), and I also needed AQ spades for the Comets on the amp side. Finally got some, tried them out, but thinking I could sell them off for a nice profit since they were thrown in with the speakers. Well, hooked them up, and it was one of those ‘wow’ monuments. I knew I could not go back the WE cables. They have been installed since, and are not going anywhere.

Cables, given the overall equipment, can make a big difference, but I think speaker cables can be even more dramatic than interconnects…..overall.