Morning, 2011...could be the original 2 Valve engine 1200 or the new 4 valve 1200. It's easy to tell, the 2 valve has a fully alloy valve cover, the 4 valve has a partial black cover that goes over the valve cover.
The 4 valve is up on power from the 2 valve from 95bhp to 105 bhp I'm not sure about the torque figures, but BEWARE. The 4 valve 1200 had an inherent problem, it could eat the valves, the 2 valve had no such problem.
If it's the later 4 valve, personally I wouldn't touch it unless it's been 'Rollerised' (plenty of info on the internet about this)
As for value, as usual it all depends on condition, service history and how it rides. I've ridden a fair few Breva based 11 and 1200's it's amazing how different they can be. Tyres can make a big difference on Guzzi's.
Price...which is always subjective, but based on the above, could be anywhere between £2700- £4500. The Norge, although a great bike, is not one of the most sort after Guzzi's and some real bargains can be had. For a 2011 2 valve 1200 in really nice condition with comprehensive service history would be somewhere between 3-4k on a private sale. If it's nice, start the negotiations at 3 and see where it goes. Good luck.