Preamp tubes in power amps

I’ve had tube gear for a decade but never, until recently, looked into how it functions or how to optimize it. So, my basic question is, my Rogue Magnum M-120 monoblocks have their power tubes, and then also a couple of 12AU7s and one 12AX7.

Would replacing those with NOS higher end tubes like a Seimens or a Mullard have much benefit?

Or would my tube budget be better spent replacing the new production 6922s in my BAT VK-3i with some higher end NOS tubes?

I figure I can’t afford to replace the power tubes until they die. But looking to see where the best bang for the buck would be on the preamp tube side of the equation.

Thanks to all who answer the actual question!