I googled this question to find out what people think about internal wires since I'm faced with a dilemma. The first hit brought me to this forum.
My dilemma is that I have these Polks RTi A7 tower speakers that sounded good stock. A bit bright and the voice a bit too much in your face, but otherwise good. They're entry-mid tier speakers but they have potential. Since I got them for free I figured I should upgrade the crossovers with some better caps so I chose Jantzen mid tier caps, about $40 per speaker. I converted one speaker first and figured I will also change the 16ga internal wire to some 12ga monster speaker wire I had. I did it because I had the wire so why not.
A/B'd stock and upgraded speaker and they sounded like 2 different speakers. Not going into sound differences now, let's say I liked the upgrade and moved to upgrade the second speaker. With the second one I got lazy and figured I'll leave the stock internal wires instead of the monster cables since I had a hard time fitting them in the first speaker.
A/B'd the speakers again and to my surprise they had very noticeable sound signatures. Monster speaker had a lot more bass, the sound was fuller, the instruments which were behind the voice before were brought up in line with the voice, coloring the voice a bit. The stock wire speaker maintained the voice forward, had significantly less bass and the sound is more spacious.
This difference is very apparent when switching them back and forth with a switch and placed side by side facing the listener. I'm not an audiophile and do not believe in cables.
My dilemma is that both speakers have their strengths. Put my family through the ordeal of a/b'ing the speakers and the consensus was 55/45 in favor of the stock wire speaker. In their words, the stock wire sounds like a live performance while the monster sounds like a studio mix with everything more balanced. The 10% difference is in their preference, not the difference in sound. I find the difference is a lot bigger than 10%.
I suggest people to do this test themselves on their speakers and invest in a switch so they can switch in the middle of the song. Only then a normal listener would notice the difference different components make.
Again, I'm not a believer in cables and I'm still surprised at the difference between the speakers in this test. Four pages of people's beliefs without actual testing is a bit of a wasted time if you ask me. I wish more people would post actual tests they've done. It would help more people make a decision in the future.