For those of us who don't play harmonica...can you detect any better sound on a high end harmonica?
Or is it just better build quality?
The sound is better...or, perhaps I should say, the "playability" is better.
A good example is that E flat harmonica. E flat is quite a high key (in harmonicaland). Normally, at the 9 and 10 holes (B flat, A flat, E flat and C) you have to stuggle to get a good tone. Notes in these holes tend to be squeaky and have unpredictable response...which is to say that you often have to blow a lot of air and then they will suddenly jump from dead silent to overly loud. With a high quality harmonica, these notes will have an even, predictable response in that they will produce a good, quiet tone with a miniumum of air and they will slowly become louder without changing pitch as you increase air pressure.
High end harmonicas are analogous to high end cars. With a harmonica, 90% of playing takes place in the middle holes (3 through 7) and any decent quality harmonica will handle that just fine. It's when you start getting to those limits outside of the normal playing range that you start to see the benefits of a more expensive, high performance instrument.