I think that with tube amps being such a niche item within a niche hobby (audio), in the grand scheme of things, little difference will be seen if tubes stay or disappear in terms of overall electrical consumption.
Rolloff rate below cutoff can show up the difference. A sealed box will roll off at a slower rate than a vented box design will once bottom of the frequency response range is reached.
My impression of ESL's is that flat ones are very beamy; step off to the side of one just a bit and the highs disappear. Curved ones may prevent that. I've never heard a curved ESL, so I don't experientially know.