Do speaker cables really make a difference ?

I second the solid core wire. Even better is magnet wire. Insulation is the key. Stored energy in the insulation (dielectric constant) is the issue. 

From Electromec

"UNWANTED ENERGY STORAGE IN CABLES – DIELECTRIC CONSTANT"

KEY TAKEAWAYS

• A wire’s dielectric constant is related to the energy stored in the insulation.
• Lower insulation dielectric constants are preferred for high-speed data applications
• This parameter must be tightly controlled for impedance-controlled systems.

@thyname I love Venn diagrams, I just love them.  No really I do. 

@zlone If you wanna stop messing around with entry-level cables, buy these Acoustic Zen Satori cables at a great price and go to the next level.  If they don’t work out just turn around and sell them at little/no loss as there’s a fluid market for AZ cables.  Just do it.  You won’t be disappointed. 
https://www.usaudiomart.com/details/649912537-acoustic-zen-satori-shotgun-speaker-cable-8ft-spades-at-both-ends/

Buy any good quality and you are done. One song with different download source can hear a different sound why they can’t show one cable sound louder than other :).

As with all things: yes, within reason.
In my humble opinion, only two criteria to watch for:

- diameter of the copper wire: wider = less resistance

- length of cable: shorter = less resistance.
That’s it. You don’t have to spend a lotta money for that muffler, err … cable.