This is an interesting watch, being from a family ownership. And like everything, its only interesting at the right price.
The dial and bezel are not the most attractive, and so it will be hard to get a high price like the 15,000 sterling / nearly $20,000) suggested above.
The dial is hard to judge in the photos, and it might be better in real life, in which case my estimate below will be more. However as it stands I see thin, greenish plots and a dial with a mark on it. If the mark can be removed, the plots better in real life, and the dial looks attractive in real life, then the value will be more.
This is exactly the kind of watch that non-buyers will place an overly optimistic price on, potentially leaving the seller disappointed by any genuine and realistic offers that might come their way.
What this watch has going for it is that it looks correct, original and has the history. Once it is serviced and cleaned it will lose a little of that visual confirmation, though it will look nicer.
Selling a watch like this has become harder for an outsider/inheritor. The big auctions have got quite snobby about which watches to take. Ebay has become much less interesting as taxes on private sales is introduced in USA and across borders - let alone problems of payment for $5,000+.
Some of the second tier auctions might be quite good for this. Fellows, WOK, Bonhams, maybe Antiquorum.
Some direct advice to the owner:
You do not say which country you are in, so I am thinking you are in UK or USA.
Do not service it, as that will lower the value. Or at the very least you reduce the number of people interested in it.
Go and talk to the auction houses, (or send an email) and they will advise you. Once you have a price from them, you can then review the private offers you receive and balance the advantages of selling privately, (more money, quicker payment) against the security and excitement of an auction.
What you have here is not a diamond in the rough. It is (as you point out) a worn and tired example of a desirable Speedmaster in original condition. It has some quality issues with the bezel and dial and so at auction I would expect it to sell for between USD$ 7,000 and 12,000. Plus fees, but you will get the figures I quote, the Auctions will get 20 - 25% on top.
So much uncertainty in those photos, too much to give a more accurate assessment.
