HOW CRITICAL ARE JUMPER CABLES

If the wire guage of jumpers is so important, wouldn't the same apply to fuses? Based on cable theory the thin fuse wire would act like a blockage in a water hose, slowing the flow.

If? Good one.

Personally, I never drive anywhere in winter without jumper cables in the trunk. 

I have tried a lot of home brew and cheap manufactured versions of jumpers on several speakers.  I have also experimented with attaching single run wires to different terminals on the speaker:  1) different jumpers sound different.  2) price is irrelevant. 3) what sounds best depends on your amp, speakers and cables.

So no one can tell you what will sound best in your system.  I suggest starting with decent bulk cable and cut short lengths with bare wire ends and adjust configurations to see how that sounds.

It depends on how revealing your system is and whether you're simply jumping biwire speaker binding posts. But for sure, if it has stamped crap metal jumpers you should hear a big improvement

I have Emerald Physics 3.4s with outboard XOs. They include some of the cheapest jumpers, which really detracts from the 3.4s hidden potential. The included jumpers are also short, which means people are leaving the XOs on the speaker bases, which vibrate like crazy. I replaced them with high quality 2ft jumpers so I could get the XOs off the bases. The improvement for a couple hundred dollars is/was... jaw dropping. These speakers deserve better