My experience with vintage gear is that a bad/cheap rectifier tube can cause problems/bad sound, but a good one just makes the system work correctly (i.e. it doesn't enhance the sound quality). Power tubes, on the other hand, will have a significant impact on your system's sound signature (different tube types will boost/diminish bass response, while different tube brands/qualities will change the clarity and tonal response).
Again, this is my limited experience with a 1950s amp. Oh! and I definitely agree that the biggest enhancement in overall sound quality comes from rolling the input gain stage tubes!!