Why do you think Bi-Wiring improves the sound ?

Unless Vandersteen knows what your amplifier or wires are, there would be no way to predict the outcome, based on the rest of what you wrote. Products often incorporate designers "beliefs" which may or may not agree with reality.

I’ll trust the speaker designers’ opinions - ON THEIR OWN SPEAKERS. If Vandersteen has designed to benefit from bi-wiring, then the speakers might benefit from bi-wiring. If Dynaudio says "do not bi-wire," they probably won’t benefit from bi-wiring, no matter what Vandersteen says - after all he didn’t design the Dynaudios.

FWIW, I build my own loudspeakers.  The most recent pair, a 2-way, has the woofer and wide-range driver on two separate boards, isolated from one another. To my ears,  they sound best bi-wired. 

I didn't see any benefit from bi-wiring.  Active bi-amping, on the other hand, with my Magnepans (built to biamp) was a huge jump in sound quality.  Literally, veil lifted off.  

^^^ Did you measure the frequency response pre / post?

No,  but it was really obvious, no need, not at all subtle.  I'm not a tweaker or believer in fancy cables, gold plated power connectors, any of that crap.  But bi-amping is a substantially different equipment configuration that is naturally going to sound very different.  Part of it is I think the 30-year old crossovers in my Maggies probably need refreshing, and so using an active crossover is a better bet.