Good idea.
I prefer the actual impedance compensation circuit, but a large value resistor in parallel with everything, as you describe, is a much simpler approach, and can probably make a worthwhile net improvement in speaker compatibility with a tube amp. (I say "probably" only because I haven't tried the resistor-only approach you described, but it looks promising "on paper".)
And I echo your caution to keep the thermal power handling of the resistor fairly high. I was advised by an engineer who designs prosound woofers for a major driver manufacturer to down-rate resistor wattage specs by 50% for high-duty-cycle applications, which imo would include being paralleled with a fullrange loudspeaker system.
Duke