Well Simon, at the end of your rationale, you mention 'outhandle'! Now I have no idea what that means. Perhaps it means if you ride as fast on the BM as on the otherly suspended bikes you end up in a hedge! Which is where I started! As I said, almost any decent shocks are better than the BMW (or any other marque) stock shocks! But if yer arse can't tell the difference, then there is no difference!
You have to start with a specific problem statement about your specific bike, otherwise you are just doing bling or chucking money blind at the bike! And that's OK as long as you acknowledge it!
All the guys I have ever ridden with who can leave me for dead on better suspended bikes can leave me for dead on a moped with flat tyres! Rossi I am not. A 'development' rider I am certainly not and I have met about three in my time, not counting shock builders and race teams! The K has no more performance than a 250 if you never open the throttle quickly or wring its neck!
I can't speak for pillion attitudes toward better shocks as I've only ever done about 400 miles on a pillion.
To define the problems of poor shocks compared to good ones you have to use words like harsh, or stiff or soggy or bump-thump or bottoming or topping-out or wallowing or chattery or other wonderfully technical terms. If your existing shocks aren't giving you any of those symptoms that YOU can describe, then YOU probably won't notice much difference with better shocks and if you lose the ESA functions you use a lot then the trade-off may not be worth it!
I have a friend who decided that his Audi RS2 was getting old and soggy and it was! He sent it off to get 'fettled' and the guys who knew his Audis was only going to put new stock bushes and shocks on the beast but my mate wanted the whole 'BTCC' hog so in went stainless Rose joints and track rod ends and much stiffer and lower suspension with 'some' adjustment (from 'ouch' to unmentionable). The car was as undriveable when he got it back as it was when it went in but for completely different reasons!
More money and time saw the builder's recommended stock stuff going in and the beast was transformed! Lovely! Sweet! OH MY GOD! Just perfect! Nothing wrong with it at all! What the builder knew that my mate didn't was that he didn't really drive it like the Porsche-beater it was because he couldn't really describe what was wrong with it in the real world, just 'not like it used to be'!
Now no-one is suggesting we all go the racing suspension route cos race tracks don't have pot-holes and race bikes don't have pillion seats but I maintain that if YOU don't have a problem with YOUR bike other than 'it hasn't got Wilbers/Ohlins/WP suspenders' then I merely question the question!
There are a couple of K owners in here who have gone the Wilbers etc. route and I am sure at least one will let you have a test ride to see the difference. If it knocks your socks off you know the answer! If you can't tell the difference, you have a different answer!
Brian (who thought his stock ESA shocks were a bit old and 'crashy' on his K12, and they were, so had them re-built by a guy who lots in here rave about and they are no better than they were, at least to his arse
)