Personally, you want a distortion. Not many out there witha tube in it, markbass do one. Although it's 12v (IIRC).
You coould find an amazing distortion pedal you love and make it better with a tube pre. The DHA things get good reviews, even sticking a T-rex squeezer after it will give it the vavle sound.
What you are refering to is the harmonic distortion you get with tubes, and to me they just sound better compared to any other kind of preamp, SS, FET etc. Although some will argue that a good SS will sound just as good, it's still not the same.
I'm after a ~SVTIIP atm to add more preamp tubes to my signal path.