just off the top of my head, the work each amp have to do is simplified - there are no crosstalk(vertical) and each speaker have its own power supply. there is reduced back-emf meaning, the woofer doesn`t interact with the same amp as the tweeter and/or midrange(the inertial energy of the bass driver vs the mechanical damping of the cabinet/driver vs the electrical damping of the amp/crossover). the power overhead is increased somewhat, particularly for the midrange/tweeter. in a vertical setup.. the speaker cables can be very short. what can be measured here probably varies with components used.
my personal opinion is I don`t think one should go out and get a couple of expensive amps for passive bi-amping. but getting another amp 2nd hand for example, or two very affordable ones can make sense
I suggest you have a look at The Superposition Principle as to why what you mentioned doesn't matter.
Further to the Superposition Principle, as to power overhead, that doesn't change as each amplifier still has to supply the same number of volts to each loudspeaker, so there's no power saving, unlike with active biamping where there's a clear voltage reduction from each section over full-range amplification. This does of course require the amplifier to have decent power reserves, if it's so marginal that the tiny (relative) power taken by the tweeters affects the bass, then the solution is one better amplifier, not bi-amping.
Loudspeaker cables indeed can be very short, although I don't se how length matters, as it's loop resistance that matters, so if the cables are long, just make them thicker.
As to back-emf damping, that's not changed at all, as the woofer's back-emf still has to go through the passive crossover to get back to the amplifier's presumed very low output impedance. Again a benefit of active bi-amping over passive.
As I said before, I can't think of a single benefit of passive bi-amping except to the dealer who gets to sell another power amp and some more 'speaker cables, both unnecessary. Either stay single-amped passive or go fully active. Anything else is a total waste of time, effort and money.
S.