RJT,
As Fatal says, there was a redesigns of cam (to try and address the comparatively weak mid-range),and a more comprehensive re-design inc dual lambda and airbox set up post 2011 when the fuel tank was enlarged massively to 23 litres, probably the other biggest "failing" on the earlier models. Yet another cam along with the new airbox set up improved the mid-range performance (and economy) again, now pretty much on a par with an airhead r1200gs in relative terms, along with a load of other changes.
The flat tappets that can cause problems if poor oil/infrequent changes and internal condensation combine (allegedly, no one seems absolutely sure on the cause as it is sporadic) was modified yet again on this "mark 3" stelvio and apparently failures are rare/non-existent. That's just my understanding, lot of info on Guzzitech as has already been said. If a full service history is maintained Guzzi will pay for the parts to upgrade any failed flat tappet model to rollers (punter pays the labour) for life of the bike. The rollers was primarily a noise thing (they are quieter) and to kill any last remnants of tappet issues, happened around early 2012 but not at the same time as the "mark 3" bikes came out, a bit later.
Mine is a 2012 NTX "mark 3" big tank model but on flat tappets (albeit the latest design of these) for example.
I also had a centre stand changed a part of a recall, no idea why?
I think misted up instruments pretty much nailed, certainly never been an issue on mine? I would rate build quality above current BMWs (and I've owned a few modern GSs and new Guzzis). The issues I've had with mine is the hella (German) spotlights - well known for failing and warranty claim, the (German or Austrian?) Trax panniers leaking (seems to be a lot better/cured with silicone grease smeared on seals and possibly design changed on newer bikes I think) and some corrosion on the zinc plated parts on the pannier frames. - not a long list in nearly 3 years and my previous Guzzi 1200 sport was equally well behaved!
One question, if not trading in, why buy from a dealer, there are a few private ones around a LOT cheaper which allows you to get the later ones within your budget? I am probably going to be putting mine up for sale in next few weeks and there are others about, these things are an absolute bargain compared to a GS say? If you are part-exing ignore this of course!
I'm only selling mine by the way as I can't justify a modern bike alongside all the classic stuff I have and don't get to ride (a 20 month old daughter has curtailed riding time severely!) and am going to try and use my 1980 Guzzi T3 california as my "everyday" bike.
Good luck, you won't regret it if you do get one..
Dave