While I agree with a "no, not in general", I have a first-hand experience with doing exacting that: spend almost as much in tube upgrade as in the original price of the equipment. I bought a Yaqin MS12-B preamp for $200 and while decent with stock tubes, I felt the urge to upgrade to Mullard Platinum and other goodies for about $150. Result: spectacular, both as a phono and a line stage, truly mesmerizing and competing-kicking ass with some well-regarded preamp costing up to 5 times my total final cost which are noisier when they are not inferior sounding to mine.
Can excellent tubes transcend modest amps?
I am wondering how far a good but not amazing amp design with decent parts such as Antique Sound Lab AQ1003 DT or a Jolida 302B can be improved by putting top notch NOS tubes? In other words, is it worth buying a used $500 integrated and give it an extreme tube make over for $200-400 rather than buying say a PrimaLuna or Cayin in the $800-900 range with its stock tubes?