I am also curious about which guitar you opted for. And I find the point about the intonation around the 5th fret interesting (never thought of it).
ps: I am an amateur guitarist, and so I will never go beyond a certain level.
Maybe I shouldn't have brought up the intonation issue because it's a bit of a black hole that can suck the light out of your enjoyment of playing if you obsess over it. I'm also an amateur and don't expect anyone will ever pay me to play for them, but I do enjoy playing with a community ensemble once a week and we give public performances 4 or 5 times a year. I've found that intonation problems that are perfectly acceptable to me when playing solo become excruciating when playing the same line with one or two other guitarists, especially if I'm the one whose Bb is 22 cents sharp. This may or may not be important to you, but if you're interested in learning more about it I'd recommend starting with the information on Sebastian Stenzel's website. You might also want to look up the well-known article on intonation and compensation written by Greg Byers in the late 90s.
I absolutely agree with CG-phile that what you really want to concentrate on is the musicality and expression you can conjure out of an instrument. I also agree that "any good quality instrument should meet these criteria" (perfect intonation, no buzzing or wolf notes). Unfortunately, my experience has been that about 1/3 of the guitars I tried in the five to eight thousand dollar range had unacceptable flaws in these areas that immediately took them out of the running.
'What issues are most important to you? What do you hope to achieve by buying an expensive "concert" instrument?'
I am after one that sounds truly beautiful (and the aesthetic of the sound is already something difficult to describe) and which is "easy" to play. The sound is probably the first most important criterium for me, after which I look at the intonation (you raised an interesting point!) and playability.
I think most of us are after that beautiful, elusive sound first and foremost. What ultimately sold me on my current guitar was rich, buttery trebles with subtle haunting overtones, especially in 7th and 9th positions. My understanding is that this is the hardest part of the sound for a luthier to get right, and I certainly played many more guitars with great bass than with good trebles.
As for playability, I've found that this is an area where most luthiers have no trouble at all. I can't recall trying a single high-end guitar that didn't feel comfortable after a minute or two of playing. The only exceptions were the old Ramirez 1A's that are noticeably more difficult to play for those of us born without Segovia bear paws. My experience may not be the norm in this area as many people seem to find big differences in playability that, frankly, elude me.
Naively I would hope that a better guitar would allow me to improve my playing, technically and not: this is the ultimate goal in the end i.e. be able to play better, as well as be able to approach pieces that were too challenging until now.
I don't think this is naive at all if for no other reason than that you're likely to play more if you fall in love with the sound of your own guitar. I've had my new guitar for a couple of months now and I still marvel at the beautiful tones I'm able to get out of it. I don't see how it can help but make you a better player to play an instrument capable of producing a wide dynamic range and rich shades of color with a beautiful timbre.
JStroud asked what I tried and what I ended up with, so I won't keep you in suspense any longer. I won't mention any of the guitars I didn't like as I'd hate to harm someone's reputation based on a single sample that might not even be representative of most of their work. Some of the guitars I did like and could have been very happy with were made by (in no particular order) Christoph Sembdner, Sebastian Stenzel, Richard Howell, Peter Oberg, Pepe Romero, and Fritz Ober. However, the one that stole my heart is a spruce top with CSA rosewood back and sides, Rodgers tuners, and the coolest rosette I've ever seen made by Oscar Trezzini, who happens to based in Lausanne, Switzerland, not too far from where alexphyd lives.
Of course, there are so many great luthiers out there (including several who hang out on this forum) that's it's nearly impossible to try everything. The list of guitars I haven't played and would like to is much longer than the list I have played. At some point you just have to trust your ears that you're hearing something special and take the plunge even if you might eventually find something you like better.
Here's a picture of the rosette on my Trezzini.
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