I think the question is really whether notes are wasted or not. For example, with Yngwie, I can't get into it musically. It just seems like the notes are there for the sole purpose of cramming as many notes as possible into a given period of time. When people say he shows off, I dont think it's cause they're jealous, like many Yngwie-heads would have you believe, I think its because they are recognizing that he often emphases difficulty of execution over the musical effect that the notes have. Even when he improvises, he never will step slightly out of the tonality, its all either chromatic, or totally scalar (i.e. no passing tones.)
People like satriani also get critiziced for showing off, and I never really understood that. For one, the fact that he uses legato gives his fast playing a much more fluid, less in your face sound, which I like, as opposed to the machine gun 200 bpm sixteenth note alternate picking. Also, most of the time he's playing very melodically, he's into catchy phrases, rather than mindless speed licks. Listen to his self titled album and just tell me it's self indulgent and not an interesting album. Try not to hum "morrocan sunset." Vai too, listen to a song like sisters, and try and find him "showing off" just once. The song didn't require any fretboard acrobatics, so he didn't put them in (and coincidentally, that's probably my favorite song of his.)
One thing i find interesting is that there are a lot of jazz players who are capable of playing as fast as most of your 80s metal players. However, when you listen to somebody like Jimmy Bruno, (one of the best jazz guitarrists around imho) it probably wouldn't even occur to you that he's trying to display his skill. Jimmy Bruno, unlike Yngwie, will often go through a whole song without any passages that are incredibly diffcicult technically. Then you listen to the next song, and theres maybe a five second run that shows you that with a day's notice he'd be able to put on a pair of spandex pants, whip out the hairspray, put a couple of pairs of socks in his trousers and shred with the best of them. He doesn't need to "show off" by playing fast all the time because he has a much better grasp of how to use chords in soloing, improvising using swing (leading/lagging the beat, as well as playing swing eigth notes) and playing over changes in a way that rock players don't. I'm not saying jazz is better than rock, I'm not one of those people. Like I said, there are lots of "shred" players I appreciate (the three from G3 are the ones i tend to listen to.) I'm just saying that playing fast doesn't have to be showing off. You're only showing off when you play something simply because you can play it fast, regardless of whether or not it is worth playing.
What bothers me is when people think that playing scalar passages and sweep arpeggios at 200 bpm is somehow the pinnacle of technical achievement just because its fast. There are country players who can do things with pick and fingers that no shred guitarrists can. Same goes for classical guitarrists with just their fingers. Also, listen to joe pass, he would fill up musical space in a way that simply can't be done using only a pick. For that reason he'll probably sound better unaccompanied than any non fingerstyle jazz/rock guitarrists.
I play with a pick, and I practice scales and sweep arpeggios with a metronome, i'm just like you guys. My point is, theres a lot more out there, and that nobody should ever think that they've mastered the guitar, because there's no such thing. No matter how good you are, (which means more than how fast you can play) theres always more to learn, theres always something that somebody else can do that you can't, even if you're John Petrucci/Steve Vai/(insert name of "guitar god" here.)
ps. Sorry I go on these rants, i get started and just cant stop