Well, thats a good question. I think "good enough for onstage" and "Good enough to be heard forever" are two different things, for one. Kirks comment about the Suhrs is that even though he's not in a business relationship with them anymore he still uses the two guitars he has from them to record with in the studio...he does a ton of session work and having instruments that are just more accurate in terms of intonation are probably very important. Sometimes you don't realize what a problem an instrument is until you are recording and everything is in tune except for one chord inversion up the neck. Live thats not too big of a deal but once you've recorded it and it needs to sit in the track next to a synth or something that is 100% in tune you start having problems.
Also, if you have a great instrument that is too valuable to take on gigs then probably you spent the money on something that sounds pretty special to you. I'm another guy who doesn't travel much with his instruments (I have a few out of town gigs coming up this year but they are all a days drive away or less). One thing they were discussing off camera was that Kirk had an L5 that changed drastically in terms of tone after a trip to Italy and back and a few other guys have had that experience. I would think that if you are in a bus going slowly from climate to climate its not that big of a deal but these guys do short trips from Southern California to Northern Europe and back, to the Mediterranean and back, to South America and back....sometimes a couple of trips to different climates in the same month...I'd imagine that would be pretty hard on any instrument.