Tubes add compression, harmonic distortion, and a high frequency roll off to the mix. Most of us just love it, i know I do. The technical and subjective reasons for this apparent contradiction takes a bit of study and open mindedness.
Yes, to some extent. In general, the closer tubes get to the speaker, the more 'tube sound' you can expect. A tube amp will give you the most 'tube sound'. A tube preamp w/ SS amp will give you some 'tube sound'. A tube source with SS preamp and SS amp will give you a bit of 'tube flavor'.
Chaos theory suggests that a tube preamp, especially one that employs zero feedback, will actually get you a better noise floor. Not- mind you, a quieter one necessarily, but one that is more pleasing to the ear.
In addition, it will have less of the harmonic distortions (in Chaos Theory this is known as bifurcation) that interfere with how the human ear processes the volume of the sound. In a nutshell, it will sound more relaxed for a given volume.
Another phenomena of tube preamps, especially zero feedback preamps, is that despite having the same bandwidth as other phono sections, you will experience less surface noise from the LP. Again, Chaos Theory explains why- with no feedback there is no bifurcation of high frequency events like a tick or a pop.
Fun stuff huh?
All components add distortion. I am with Atmasphere: Some distortion interferes with the hearing process more than others. Some distortion even improves the process. Adding echo to the sound of radio voices, for example. Compression is often desirable when listening at levels below the original - which is all the time.
Tubes do it best.