below 100hz, do speaker cables matter?

I think it does. Especially if the woofer is inefficient. Heavier gauge speaker cable has less resistance. Longer runs require heavier gauge to minimize resistance. I recently tried Kimber Kable 8 PR for the bass modules of my VR-4JRs and the bass is deeper and better defined.

Bass notes have harmonic overtones that are directional. And the quality of cable certainly does make a difference both in the fundamental bass note and its harmonics, IME

Every time I've upgraded speaker cables the bass has improved as much as the mids and highs. I vote yes.

Yes, more than for other frequencies in most cases.

My argument lies with voltage divider effect, eloquently explained by Al (Almarg) in this thread http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1336159920&openflup&3&4#3

Given that most speakers exhibit their lowest impedance in a range below 100 hz, it would follow that the impact of cables inductance would be the greatest on the bass notes.

Also the omnidirectionalality of bass frequencies has to do with the propagation through air and not of the signal in cables. So the fact that bass is omnidirectional and mids and highs are not, IMO should have no bearing on cable design.