Do speaker cables really make a difference ?

Yes, in my case cables used anywhere in the system have an effect on sound. Including speaker wirings and even the electronic PCB cards tracks have an effect. I had an old tube preamplifier I disconnected all the PCB tracks and replaced them with point to point wirings. The sound improved a lot.

If you want to test try these tow cheap cables below recommended by Whathifi. Try them separately first and then both connected in parallel (Make sure the cables get enough burn in time first). The Clearwater is good with treble while the Rocket is good with bass. I use them connected in parallel.

Van den Hul The Clearwater and AudioQuest Rocket 11

Even the wires in the crossover coils have an effect. I replaced the LF filter coils with Jantzen Audio WaxCoil 12awg and the sound got better. I will replace the rest soon, I had already replaced the capacitors some time ago.

Post script: 

I got some anticables many years ago and they sound fine.

As previously remarked: at some point accept happiness in how your system performs.

Unless you have access to exotic conductors, the 'amount of metal' (i.e. gauge) of the cable/wire is the best measure. That having been said, if decent gauge lamp cord isn't good enough for you, paralleling 2 or 3 strands ought to do the trick. Thank you Dr. Ohm. If you are concerned with increasing capacitance(?), a cable containing the same amount of metal as the 3 lamp cords would have the same capacitance issue. Electric current is remarkably disinterested in other details except for loops in the wiring and oxidized connectors.

The confirmation bias story I like best:

A man was walking in Manhattan with a bag of salt slung over one shoulder.  Every few yards he took a pinch and threw it over his left shoulder.  Someone came up to him and asked him why he was doing it.

'Keeps the elephants away.'

'But there aren't any elephants for miles around here.'

'Effective, isn't it.'

That has to be the most dumbass analogy that I have heard on confirmation bias. You folks don’t realize such known and true cognitive disorder works both ways. By definition, confirmation bias is the tendency we as humans have in seeking information and facts that confirm existing beliefs, rather than questioning them or seeking new ones.

Yes, people who believe speaker cables make a difference are not immune from confirmation bias. Let’s be real, all humans do. But, whatever they believe, is based on actual experience, and ownership of said cable. By definition, experience and experimentation ARE in a way objective facts. The “elephant” they actually “saw”. You on the other hand, base your opinion generally on stuff you read on the internet. The “elephant “ you never saw. So, who is the most “sick” from the cognitive dissonance ?

Another observation I have from “following” naysayers on audio forums: you spend so much time, energy, and effort in an attempt to “prove” what does NOT work. Debunk and disprove stuff. And almost none on what actually works. Why? Perhaps that way, by sharing YOUR experience on what works and how and why it works, you could become more useful to the Audio community? Actually contributing something