Actually you can push this topic even further. Instead of just looking at how the guitar works with the other instruments in a band, why not look at how all of these things add up to what it was designed originally for, that is to make music.
I also can't find fault in someone buying all sorts of gears be it a new guitar, amp, pedal, etc. I myself have been guilty of that. But at the end of the day, when we are actually playing music using our gear, each component's importance to the whole scheme of things becomes less important. What use it is for someone who has all the best equipment money can buy when the most music he can make out of it is mediocre. Of course, there are people who buy gear for the sake of buying them and collecting them, but then that's another topic for discussion.
In other words, people don't get famous because they have good tones, or transparent guitar sounds. People get famous because they play good music not because they have good equipment.
Another thing is sometimes people forget how quite a few of these guitar gods came up with their tones, mostly I assume was based primarily on what equipment was available to them at that time.
Having great gear is not a bad thing I suppose, but having it and being able to use it for what it really was designed for, is far more important for me than anything else.
Now going back to the actual topic.
I know exactly what you mean DB. Whenever I get/buy something for my rig and coming from past experience, I always try to approximate how it would sound in a live environment in relationship to the rest of the members of the band as well as the music we are playing.
One of the things that has been of great help to me the last couple of years or so is recording everything "off the floor" whether it is a live gig or a rehearsal. Like you said what you hear on stage is normally not what you hear offstage. With the recording, it gives me an opportunity to find out what needs to be improved on as far as my guitar playing is concerned. Be it a simple change in the way I do the rhythm parts to how the solo works out or not and yes if I'm pleased with the kind of tone that comes out of it.