Passive BI-Amping does SOMETHING, the question is whether that something is worthwhile. Generally not, but if you have the equipment, Bi-Amping is certainly worthwhile for the experience, and then you can make up you own mind.
Myself, out of curiosity, I tried it using two Integrated Amps, one pre-amped to the other. I never heard my speakers sound better, but I think that was not down to Bi-Amping but down to the unique characteristics of the Amps I was using (Mid/High = Onkyo, Bass - Yamaha). As good as it sounded, it was impractical for me, and my regular Amp (Rotel) gets the job done nicely.
So, if you have the equipment, it is most certainly worth trying, and then you can decide for yourself if it works. Knowledge is never wasted.