Now that is a classic beauty. The movement inside is most likely calibre 8531,
the dial looks like it was made in the early 60's.
Take it to a good watchmaker (not one of those who only knows how to change a
battery). Unless there is something seriously wrong a basic servicing should
cost you a few hundred euros.
Ask the watchmaker to note the serial numbers in the back of the case and on
the movement, with these we can tell you more. There might also be a model
("reference") number inside.
I don't now the sales value, but if you surf around on ebay and other sites
you can get an idea. But if it was mine I would definitely keep it.
Best regards,
Henrik