To bi-wire or not to bi-wire?

Sounds like you already have the proper approach and are a rationale consumer; as evidenced by your comment about the Wilson Cubs. Biwiring does not make any sense from an engineering standpoint. The theories used to support biwiring are pretty much junk science, particularly the idea that your amplifier sees a different impedance when driving the same speakers biwired vs non biwired. I have not heard a difference between the same pair of speakers biwired or not. Biamping on the other hand makes a good deal of engineering sense and if you really want to tweak your system for noticable effect, is something to be considered. This of course is more expensive. More importantly, biamping with off the shelf units requires a good deal of research before-hand as to the units and requires some experimenting once tentative choices are made. The ideal way to biamp is to design the amplifier specifically for the driver. Speaker wire is not all that expensive (unless you subscribe to the idea that expensive speaker wire is better) so trying biwiring vs non biwiring seems reasonable. Even if you do subscribe to a theory or expensive speaker cable is better, experimenting with dollar per foot speaker cable for 15 foot runs with decent connectors is inexpensive and the results of that testing should sufficiently inform you as to which choice to make.

Musicnoise...If the woofer and tweeter share a common ground wire back to the amp, then, due to the wire's impedance, each driver will see, at its ground reference, some of the signal intended for the other driver. I don't know how significant this is, but it's the best scientific reason I can think of for biwiring. It also implies that only the ground wire needs to be duplicated.

I have found biwiring to make an obvious difference in my system. However, I do agree with the reports of many people who say that it is system dependent.

I disagree with comments that it is based on junk science. If it is, then why does it work for many people?

As to whether it makes sense from an engineering standpoint, I have no comment because biwiring is based on science, not engineering. They're two different disciplines although obviously related. By the way, from an engineering standpoint, bumblebees can't fly. New engineering students in universities are often presented with this in order to challenge them not to be too dogmatic or closed minded when studying, analyzing and experimenting.

The speaker designer has provided two sets of binding posts for biwiring possibilities so they think it might be effective. Their opinion might be worth something. It may or may not work depending on other variables in your system; however, it's worth an experiment. Even with cheap, inexpensive cables, I have found it to be effective. So you might try borrowing some cables to give it a try. If it works, great. It's a cheap upgrade. If it doesn't, no harm done. It's part of the fun of the hobby.

Biamping should certainly produce an improvement too. However, my opinion is that passive biamping is not cost effective unless it is an intermediary step to active biamping.

Biwiring is explained scientifically on the Vandersteen website. It works, given that you use seperate (not jacketed) cables for the lows and highs.