Its not for me, or anyone else, to tell you what to do but I'd urge you not to sell. You've got a complete set which is unusual in itself and clearly the watch means a lot to you and I think it would be a real shame to break up the set. I can't imagine the box will ever go down in value so if you really need the cash in the future its a very liquid market and you can sell it in days - but you'll never be able to get it back. Sure, you can wait for another box to come up - but it won't be the one that came with the watch.

And by the way, your Dad's old watch is a really nice piece. I hope you enjoy wearing it.

Best of luck to you whatever you decide to do.