Why do you think Bi-Wiring improves the sound ?

No ! Many non bi-wire speakers can be designed with an L pad in the midrange and or tweeter circuit. In the Vandersteen 2 and 3 they are very carefully deployed with a very high quality device that should not be used frequently as one might a tone control. The range is significantly less than available via most tone controls. You can read more by downloading a manual from the Vandersteen website.

finally, at least for Vandersteen IF you wish to preserve time and phase, do NOT use a different wire for the two legs of the Biwire!!!
a notable exception is the new Audioquest wire that has the RF trap on the bass.

have fun, enjoy the music

Here's my short take on this:

Amplifiers are more susceptible to impedance variations than we think, even in solid state.  I think we are hearing these changes, and when you bi-wire you, perhaps to a very small amount, are changing R, L and C.

Now, the question, _if_ I am correct, and _if_ it makes a difference, is this small change worth $5?  I have no idea, but have you thought about room acoustics??  ;-)

When I build bi-wire terminals on speakers, it is only with bi-amping in mind.  Why would you add 8ft of speaker wire, rather than 3 inches in the crossover?  

FYI, whenever these discussions come up I think of MIT cables, who put crossover components into their little black boxes.  Clearly, a little inductance and capacitance in the cables seems to have sold many a listener.

@TOMIC601 where are you located?