Methinks the biggest problem with the set neck construction usually is that the woods may set a little differently, i.e. the neck woods might 'shrink' a little causing the level of the neck wood in contrast to the body wood to be ever so slightly lower than originally intended, and causing the fretboard to have a slight 'hump' where the neck meets the body. (seen that on old and new guitars, even Gibsons) And if not a 'hump' at least the section over/at the body will be flat and the natural bow of the neck happens only later on the guitar, making set neck guitar's action and truss rod adjustments more difficult and/or dependent on woods and build quality.
In terms of sustain, I don't find much absolute difference between set/bolt neck guitars...the sound and type of sustain is different, yes, the sustaining frequencies are different, but in terms of absolute sustain there are bigger factors at play...I once did this test by plugging in setneck, boltneck and also Floyd-equipped axes with identical pups into my DAW and dropped a pen on the low strings from the same altitude (same power hit) and checked the recorded waveforms for decay etc. and for some reason on the floyd guitar the resulting waveform was the longest i.e. there was most actual sustain, which was quite contrary to general idea how it should have been.
But as for the OT normal glue should be plenty good for structural strenght, just make sure you don't push the neck too low in the pocket, better have the fretboard base a few thousand milles higher than the guitar face than the other way around in a few years.
Dee
"When life's a biatch, be a horny dog"
Amps: Marshall JVM 410H w/ Plexi Cap mod, Choke Mod & Negative Feedback Removal mod, 4x12", Behringer GMX110, Amplitube 3/StealthPedal
Half a dozen custom built/bastardized guitars all with EMG's, mostly 85's, Ibanez Artwood acoustic & Yamaha SGR bass, Epiphone Prophecy SG, Vox Wah, Pitchblack tuner plus assorted pedals, rack gear etc. for home studio use.