You might get decent money for it, but perhaps not on here - RB buyers are usually looking for a project rather than a bike. Those cranks are a notable survivor, you don't see many period, let alone in good condition. As you say though, it's a pity about the Curve cantis and the other original parts going missing, as they all have a value now.
I would say if you have a back problem, the worst thing about the current spec is the tyres. Have you ever tried putting 2.25 Racing Ralphs on it? The other thing I would do is fit an ahead converter, shorter stem and 26" low-rise bars. Fitting Hell Bent bars to my 95 Kilauea (also has P2s) made an amazing difference. I really wouldn't have believed how much a bar could transform a bike's handling characteristics, but it's a far, far better bike now than it was before.