Re: There are some things I just don't understand.
I don't mean to soumd patronising, but this is an opinion that always seems to be particularly prevalent amongst younger guys. I remember thinking the same thing when I was 17-18. I wonder why that is.
I used to think the same way, and I think it's because:
1.) Many, many guitars -- including a lot of the least expensive ones -- are Strat copies. Go figure.
2.) Many of the remaining cheap guitars are copies of Les Pauls, Soloists, and other guitars known for set-neck or neck-through construction. Often, these inexpensive instruments use bolt-on necks.
Then I started seeing $2k JEMs and USA Dinkys, and $3k ESPs with bolt-on necks. Hmmm… It got me thinking that bolt-on construction isn't always chosen just to hit a price point. That there was more to it.
As far as sustain goes, it's already been mentioned that sustain itself shouldn't be a goal for a guitarist, and certainly not at the expense of things like playability, comfort, tone. Besides, of the guitarists I listen to regularly, the two who are most likely to let single notes sustain for ridiculously long periods -- Steve Vai and Yngwie Malmsteen -- both use bolt-ons. Personally, if I cared that much about sustain, I'd try one of the active sustainer systems on the market, or just kick in a well-adjusted compressor.
The topic of gluing in a neck has come up often in these discussions. I've done it four times on different (inexpensive) instruments, and in each case there was a marked difference in feel and tone. I cannot speak to how this gluing in of the neck would affect the feel and tone of a very finely crafted bolt-on guitar, and I won't pretend that I can. But on the three guitars and one bass that I did this to, it made each instrument feel more like a single piece of wood, and it made the lower midrange more prominent. Call BS all you want; I'm not going to argue with you. I'm simply reporting what I felt and heard. Sustain? I can't say it made a difference that I could tell.