I decided to shop around for a lightweight guitar amp, and the Roland CUBE 30X hit the sweet spot perfectly. Very affordable at under $250, the amp has a 10" speaker, the usual BOSS/Roland COSM amp modeling system, and weighs just under 20 lbs.
The only downside to the amp is an issue common to most small amps: an overly boomy mid-range and brittle high-end, neither of which can be "tuned away" with the basic tone controls.
A speaker-swap was in order.
Eminence makes a variety of guitar speakers, and they provide excellent performance details on their web site. The Delta Demon 10" speaker has the flattest frequency response and smoothest high-end of their selection, so I ordered it.
Wow! The sound quality of the CUBE 30X with the Eminence Delta Demon is stunning. I can't believe an amp this small can sound this big and warm. No more booming mids and amazingly warm high-end. No, this doesn't have the tube warmth of my main rig, but the sound is the best I've heard from any amp under 20 lbs.
It makes me wonder if Roland shouldn't market this amp with the Eminence speaker pre-installed. I'm blown away.