There are certainly many ways to reduce the weight, to some extent, of valve amps, but you can only go so far, as yet.
One thing that I think no-one has yet mentioned as a down-side for valves is the need to match impedances always. Unlike SS, where a 4ohm output can be run into 8 with merely a loss of output power, doing this to a tube amp will wreck the output transformer sooner or later, usually sooner.
My personal take on the whole thing? SS every time, purely to save my back! I'm certainly old enough to have been around when SS wasn't often an option!
My favourite valve amp of those I used was a Vox AC50 head. Great amp, and reliable, too. But I wouldn't have a valve amp now even if i had free roadies! I prefer not needing a big car...