certainly not worth it with the cost attached to them fully agree, but it's free fun for us in the axe. Like i i said in a previous comment here, axe normalises the transformer ratios for all tube changes and gets a different knee voltage/hardness loaded when you change the tube.
Hence the difference is not as apparent.
but playing with bias, mismatch, bias excursion, excursion and recovery time in addition to changing the tubes its a lot lot more pronounced when you change the tubes, as all of them are somewhere or the other linked with bias volatage directly/ indirectly . End of the day these are the things that real amp makers mess with , albeit in a more complicated indirect manner than axe, to extract the most out of the tubes and the amp design.
The tubes themselves have no sound but just react to the other things in the amp ad speaker side.
Certainly most people dont need to do this when axe can get lovely tones just from the authentic /ideal page, but these are important things none the less.