I'm an electronics tech trained on all things thermionic, from basic audio amps to whole radar systems. I like valves!
But compared to a good solid state amp (all considerations of tone aside), they are inefficient and unreliable, and there is, quite literally, no way to change that. If you must have 'that' tone, fine. But expect to a) pay, and keep on paying. No-one who regularly gigs a valve amp should expect to revalve it less often than once a year. In practice, they do last longer if looked after, but that's what you HAVE to plan for. The amp tech's mantra here, for a 100W Marshall, is a fiver a gig at two gigs a month, or one gig a month for a 50Watter. In terms of reliability and cost, solid state is having your cake and eating it. It cannot ever be that way for tubes.
But they do sound good!