Does the"quality" of jumpers affect the sound?

Let's assume it does make a difference. It still seems to me that a pair of brass bars (or the better copper ones) would have an excellent chance of outperforming two jumper cables of even super-premium pedigree because those cables are (1) longer -- usually 6 inches or more compared to maybe 2 inches for the bars; (2) have solder joints to spade or banana connectors on both ends, versus no joints whatsoever; and (3) are prone to higher inductance because the + and - are typically separated by a greater distance than with the simple bars.

I wish manufacturers would do away with biwiring as an option unless they are absolutely convinced it matters for their speakers (e.g., Vandersteen) or unless it is a speaker that is likely to be biamped. I also wish they would standardize on a single binding post diameter.

I'm pretty sure every manufacturer that offers their speaker in a biwire version believes it absolutely makes a difference. Otherwise, why would they spend the extra money?

I wouldn't be so sure. I think many do it because it's "expected".

Clio09 is correct. The Spendor 1/2 has two tweeters, as does the Harbeth Super HL5.