Is upgrading stock tubes standard proceedure?

There are lethal voltages present even well unplugged in some components, safety comes first!
Manufactures are well aware how careless some people can be.

For sure some equiptment respond favorably to select vintage brands of vacuum tubes however some do not as Tvad and Mrtennis point out.
They know what they are talking about...

There are a few modern companies that take the time and use the quality of materials that made MOST of the NOS tubes so good. The vast majority of those manufacturing tubes currently, are doing so strictly for fast profit, cut corners anywhere and everywhere they can, and their tubes sound like it. I got back into tubed gear/NOS tubes 18 years ago. I've yet to find a piece of equipment that did not sound more like live music with the right NOS tube upgrade. Here's a list of the companies that are producing tubes that can compete sonically and quality wise with the old stuff. Price some of the pieces and get an idea of the cost of quality manufacturing nowdays:(hhttp://www.kraudio.com/ttp://www.gcaudio.com/cgi-bin/store/search.cgi?cat=49) (http://www.gcaudio.com/cgi-bin/store/search.cgi?cat=49) (http://www.westernelectric.com/products/300b.html) If the signal passes through a tube, it WILL affect it's sound. There's no such thing as a tubed circuit that is not "tube sensitive", in this regard(the tube being the most "active" component in the circuit). Even the rectifier will have a sonic effect on the sound of most tubed equipment, although it's not directly in the signal path.

An extra "H" got in that first URL. Here's a correction: (http://www.kraudioproducts.com/Kr/ProductMain.aspx?CatID=13)

I just place my order for these two tubes Mullard CV4004/12AX7 to be used in my VTL 7.5 preamp. I heard noting but good things about these tubes... I view purchasing NOS tubes like purchasing a rare wine some may like it and others may not.

many current-production tube components have circuits which are not tube sensitive. i have encountered many examples of this phenomenon. in such cases, replacing stock tubes is not beneficial.

Going from one tube to another does not guarantee an audibly detected change. The two tubes could have very similar sonic properties. Or the overall system is dimensionally flat to not allow for one tube's refinement to shine over the other.

If you go to the extreme and try for example, a premium Valvo or Amperex pinched waist tube, and compare it to something like Sovtek or Electro-Harmonix, even the most compromised tube design will show this difference instantly. The comparison may result in nearly the same tonality but dynamic contrasts, ambiance and decays of the NOS are significant compared to the newer manufactured tubes. And no, I am not talking about "warmth". The newer stock tubes also tend to sound forward and fatiguing (edgy) compared to the far more smooth and natural result of the NOS tubes.

If the signal passes through a tube, it WILL affect it's sound. There's no such thing as a tubed circuit that is not "tube sensitive", in this regard(the tube being the most "active" component in the circuit).

Agreed.