Morgenholz will put to rest the fact that tubes in fact color the music.And how are tubes different than any other active or passive component in an audio product's internal-component lineup? Just read about the various Nelson Pass designs where a number of different solid state devices are chosen for one kind of sound vs. another. And the debate of BJT vs. JFET vs. MOSFET.
The beauty of tube gear is that many products can be configured by the owner with many different brands and tube types to dial in various changes to tonality, dynamics contrasts, portrayal of space. Can you do this with a solid state device? Obviously no. For this reason and simply that many tube preamps and amps quite handily destroy their solid state peers, in the areas of portrayal of space, I will stay with tubes any time.
Morgenholz: Try the RCA 12BH7 in your 12AU7 socket. You will be pleasantly surprised....perhaps more than the power tube debate. And these are dirt cheap on ebay. Even if a used pair, they will last a long time.