I'm going to have to disagree with most of the previous post. Yes they do vibrate, but not at all speeds, its a 1200cc V twin FFS, want smoothness buy a four cylinder bike.
I think the build quality is better than my previous GS1150 of six years ownership (the paint peeled off the engine covers and fork legs by the time it was two years old) A pal of mine who previously owned a GS1150 ADV for several years swapped it for a Stelvio. His bikes live out on the street uncovered in Scotland. His Stelvio has weathered far better, has never failed to start in five years of ownership and is now only just showing a few signs of corrosion on the spokes and some non stainless fasteners.
I find my Stelvio NTX very comfortable the bike has covered many big mileage days without comfort problems although I don't think it is as comfortable as my old Tiger 1050.
The heated grips are the biggest let down, not brilliant but adequate, fit Oxford grips instead (cheaper than Guzzi items) The later model bikes (2011 up) can switch them on the move, a very simple system.
Reliability is not an issue, I'm on my second Stelvio no problems in nearly three years. My first Stelvio bought new in 2009 had a speedo sensor failure (fixed under warranty) and also a slight misfire which was cured by fitting NGK plug caps, this bike was later used by the Hairy Bikers in a series.
I can't comment on the availability of spares as I or my two mates who own these bikes haven't needed any.
The eating isn't cramped up for me and my wife, loads of room and I'm a big twat, but my wife is slim.
I think the Stelvio is a very underrated bike, sure it doesn't have all the latest bells and whistles, but I don't want them, the simpler the better for me. What's more I find it rather fulfilling riding a motorcycle that is quite exclusive, full of character, and easy to find at bike meeting places amid the swathes of GS'es and sports bikes that every man and his dog seem to have these days.