I'll try to answer the question...
I got into tubes last year. It all started with a tube DAC and now I run a tube preamp as well.
The introduction of the tube DAC brought a few immediate changes to my previously all SS sound. The first is clearly a different sound for cymbals. They sounded more realistic with a spectacular metallic shimmer. Anything I'd call "harsh" was completely gone. Midrange and vocals seemed to sound more realistic as well. There was a distinct change in the sound stage as well. The tube DAC added a more 3D effect to the sound stage and there was clearly more separation of instruments and vocals. There is maybe more subtle changes for the positive like a complete lack of glare, but the above changes is what made me love the tube DAC. People can say what they want about tubes "coloring" the sound. To my ears, the gear I've chosen makes things sound more realistic and accurate. I couldn't listen to music any other way. There is also NOTHING "warm" about my setup.
Of course with all things in audio, there seems to be trade-offs. One trade off for the addition of the tube DAC was a loss of definition in the bass. This was NOT subtle. It actually made me not like the DAC. What's funny though, is when I tried to get away from the tube DAC, I couldn't. It was clear to me that the benefits outweighed the negatives. I later modded the DAC with Burson discrete op amps and an upgraded clock. The addition of the "right" tube, and the DAC is now spectacular in all regards.
The addition of the tube preamp didn't have as much of an impact on the sound, but it did seem to add more layers to the sound. I've experimented swapping back and forth with various components and mixes of SS and tube, but I can honestly say that the tube gear I own is staying.
I run SS amps and I don't see that ever changing as I use them for HT use as well and want the power and dynamics they provide. I think there is some magic that comes from a mix of tube gear and SS. Of course a lot depends upon the particular pieces of gear used as I'm sure there are some SS preamps and DACs that provide a similar sound quality to what I described I get with my tube gear.
From my understanding, most tube gear should provide the sound qualities I described above. I took a chance on tubes and found the pieces I chose to work perfectly for me. It was one of the best things I've ever done for my audio listening.