Tube amps and speaker wire ?

I think you are talking about shielding, not insulation. Interconnects benefit from shielding. The concept is controversial for power cords. Some believe shielding can trap RFI inside a power cord. I don't use shielded power cords, but I keep them well away from my signal cables. Speaker wire is rarely shielded. Some designs use twisted conductors to reduce inductance, which is good.
The main issue with speaker cable is to use a sufficient gauge to minimize resistance. Except for extremely long runs, 12AWG is plenty thick for most setups.
I've tried fancy cables, but this is what I use now: DIY-terminated Furez 12AWG @ 88¢/ft.

Furez 12 AWG 2 Conductor Speaker Cable Raw

To the OP: I'd stick with your existing speaker cables. You are not likely to improve SQ spending money on expensive, boutique speaker cables.

 

What about using 16g & 20g if your bi-wiring? Higher guage to mids and tweet lower to woofer?

 

Hello
Yes is a good solution. I do not know in biwiring situation,but I changed my internal wire in my speakers using duelund 16g for low and 20g for high. You can read more at jeffsplace.positive feedback.com

 

You can if you like, it won't hurt anything.

But then, I doubt if you would hear a difference.

 

If I can try something on the lower side of cost like the duelund speaker wire and experiment for fun then why not....

If I'm gonna spend a lot I'd rather buy some nos valves to roll around as I'm sure I'd get far more bang for buck....