I have now arranged my mobile location shooting lighting setup.
The first is far more mobile than the second:
1-2 Canon 580EX II speedlites
1 6' Manfrotto 5001B Black Nano Stand
1 13' Manfrotto 307 Stacker Stand
Umbrella swivels (importantly, upgraded with Stroboframe cold shoes which hold the flash much more securely)
Westcott 43" double-fold collapsible umbrellas
Triggered with a Paul C. Buff CyberSync CST and CSRB+ transmitter/receiver set with all settings manual.
If I'm going for a very lightweight setup, I'll only take the one light, with the Nano stand. The weight added by a second light is significant if I am going to be walking any real distance, and my inclination is to leave it behind when I'm not going out specifically to take photos. However, if there is much wind, the larger stand is much more stable.
This is all in keeping with the principle that a mobile lighting setup is useless if it is not carried on one's person. As soon as a setup gets too big to comfortably carry for an extended period of time, it stops being used.