IMO, 2 kinds of people want a norton. One is a collector. It isn't about riding for them, and they are looking for the most desirable or rarest models. One of the better jokes about Norton's is that the factory made 1000 production racers and after all these years there's only 5,000 left in existence... (people convert ordinary bikes into proddy racers) So the values of certain models are collector values.
The other person who might want a norton are vintage MC riders who probably were young men when Nortons were in production and are still interested in them nearly 50 years later. Most of them actually want to ride their Norton because they might be older technology, but a commando still easily joins the flow along side modern traffic. Mechanical correctness is king for this group, not special accessories like that fairing.
As far as prices go, they can be all over the map. I'm not great with valuation, but a few guys here have bought, restored, and traded in nortons for decades and they have a better handle on the value of your bike than I would. You should take the bike to a "norton guy" to get it running. If it has power, idles well, and looks as good as it does, then $10,000 seems like a decent starting price to me. If it's a "collector's model" of some sort, I would say that it could be a many thousands more. If you can't get it running then $5,000. based on it's appearance.
If it doesn't run, then you can't sell it as a "ready to ride" bike. There's definitely a market for those who DON'T want to rebuild a vintage bike, but want to have one to ride. Those people pay for a finished project. The people who are going strip the bike down, paint the frame, rebuild the engine/gearbox/primary don't want to pay finished project prices since they will put a lot of time and money into the restoration.
In the end, you might get $12,000 or you might get $8,000. depending on finding the right buyer. I don't think most people here buy other guy's finished projects, but the general public does. Guys who collect motorcycles and just want a Norton in their collection are probably your target buyer for your best price.
I have a dunstall fairing on my bike. I know it gets some weird looks from other norton owners but it keeps the wind blast down at 80 mph so I like it for that. Your fairing is kind of cool, and kind of weird (like mine) but I'd love to ride behind it to see how well it works. Although I am pretty sure I would remove it because a Norton is a sport bike and that fairing is more of a full coverage touring fairing. I think some guys might love it, but I ride my commando in a sport bike fashion so it's not appropriate for my style of riding (twisties)
anyway, Cool bike thanks for posting it.
...... Edited to add @ Greg,.... stock nortons don't look as good as this to me
In fact, the puny fuel tank on a roadster looks completely disproportionate to the rest of the bike without clip ons and rear sets. Even then the bike looks better with a race fairing like this