Bengodog, only you can decide whether it's worth fixing. As a family heirloom, you might want to invest some money in it, or just put it aside with a note about who you received it from.
Professional repair of the dial and the movement would likely not be inexpensive.
You'd want to be very choosy about the watchmaker who works on a family heirloom. Like any other field of work, some are much better than average---and some are far worse.
You seem to have done some research, as you're correct on a number of points.
The 18 and the .75 both signify that the watch is 18 karat gold. Both S.S.&Co. and S.&Co. were trademarks of Stauffer and Company a.k.a Stauffer,Sons & Company. Stauffer was associated with Charles Nicolet from 1856 through 1944.
The other markings on the case show that it was imported into London circa 1908/09.