Sorry.. I always wanted to blurt that out!...
AAanyway.. Yes that buzz you feel is normal for a lot of inline 4's and the for the 919 in particular because of the re-tuning to bring performance down into the lower rev ranges.
As stated, after market 'bars will make a huge difference.
The Renthal Ultra lows for eg, all but elimintate the 4 - 5k buzz that most annoyingly sets in at highway speeds. They do, however seem to bring in a little more vibes at lower revs, but the frequency is low enough that it's not numbing in any way.
As for smooth motors.. Personally I think the inline 4s are
quite smooth, in fact that was a major selling point for the old CB750 when it came out, it's just that the frequency of the vibes you do
get tend to be just high enough to be a bit on the numbing side and as such are more noticeable in the long run.
That said, I also have an old VF400 (V four obviously) and I'd say it's about as smooth as an internal combustion engine can
be. The only vibes I ever feel from it tend to be a very
mild buzz in the footpegs at about the 7 - 8k mark. And I only tend to notice that if the road surface is particularly smooth too. Man that thing is a lot of fun to chuck around!
They are a dog to work on while frame mounted.
You got that right! even changing plugs makes for a good chance to practice your Zen and the art of motorcycle maintenance..