In my opinion, tube preamps (or anything) are hot air. I’m not discounting their viability, but they don’t do anything special to me. I’ve tried playing SVTs in the store, but they just didn’t feel right. No immediacy in the attack. I can dial in some boom on my SS rigs, but can’t dial it out of the tube rigs I’ve played. Granted, I’ve not played many tube amps, but none of them did anything for me. SS rigs are just more my style. Again, personal preference and all that. For reference, I’m talking pretty much GK vs. Ampeg here, and as much as I used to want Ampeg back in the day, I just have no interest anymore.
Part of me also wonders about the tone goals - I typically prefer flats for the thump, but many people find them to be dull and lifeless. In my brighter and often more articulate SS rigs, they can be plenty lively. But most people prefer rounds. And with their natural tendency towards treble, may work better for a tube amp that isn’t quite as articulate. Anyway, not sure, as I haven’t tested these things, but that is my thought at least. I’m sure someone with more experience can chime in.