I don't think of playing fast as a crutch to make up for an inability to write a chord progression or melody. And lets face it, playing fast is alot of fun, for me theirs nothing like dropping down into E, and just burning it up w/ some fast funk bass. It's a blast, but that's not the sort of thing I want to do all night. The fact is I do like writing interesting progressions, and that sort of thing speaks to people better. Also, it's really hard to play w/ soul if you're playing that fast. Most shredders sound really cold to me; amazing technique, little passion. As much as I love Buckethead, theirs only one part of "Monsters and Robots" where he brings it up to that next level, and that's in the very last song, but that's what I love most about that album.
So in other words, I love to show off, but I come from the blues school of thought: nothing speaks your mind like a good bend.