There are SIGNIFICANT differences in sound reproduction by both changing tubes, and or speakers,... and for both,... it requires time to actually notice the full impact,......
By that, I mean a speaker must be broken in in order to appreciate all the subtle things it reproduces in your sound....
This is not as pronounced in cheaper speakers,....
and a change in tubes can do equally as much for your sound, depending on how much you push your amp,....
In other words,... the louder you play,.. the less noticable the enhancements are, IE:... going from a Sovtek 12AX7WA to a NOS RCA 7025, made in Holland in an Amperex factory,...... and you notice changes immeadiately,..... the Sovtek sounds thin and without charactor next to the RCA....
If you've ever time to try this,... you'd know....
Broad statements are not correct in tone assessment,... there are just too many variables, .... kind of pickups, color of music that is played ( Metal, Jazz, Rock,..etc.), circuits in the amp, type of tubes,.... size, type, and quanity of speakers,.....how much processing is done,...before the signal gets to the amp,.... or before the speakers,.... or both,.....
I hope I've totally confused the issue now,......
Steve