£650 seems about right considering it needs a bit of work maybe a complete respray,that would take it up around the £800-£850 mark,it's not just about what it's worth now but the extra cost involved in preserving it.
Confused at this statement a little too.
Does it need Repainting...?
T-Cut and Polish the frame. Strip and Polish all the components, and dress everything accordingly...? Wheres the cost...?
Even If painted. Sandblast, Zinc Coat and Powder £30.
Strip By hand, Single Colour with Decals and Postage Both ways £150.
But I Honestly cant see from the pics supplied it needs it. At most the hardest work would be to strip the wheels, Polish rims and Hubs and then rebuild with new Spokes.
With little more than effort and time, That bike would look and ride like Brand NEW.
The only thing I would definitely do is Donate the Retro "woolworths Supplied" Everyready light holders to Charity.
They seem very desirable by certain types......PMSL.