1966 Omega Sea Master De Ville- Considering purchase, have questions

I have always wanted to get a vintage Omega, and I have recently found someone who was selling one. It was her father's, and he was given it in 1968 by his company. I have figured out that it is likely a 1966.
Apparently, it has been in a drawer for the last 40 years. She has told me it is in good working order, although it has not been opened, or serviced for many years. Also, she was told that the case was gold plated (although I suspect gold-filled), not solid gold.
Obviously the band is not original, but it appears as though the face and dial are.
Is this a collectable piece, is there anything I should ask, or be aware of, and what do you think would be a fair price to pay up to, and how much would a good servicing cost? She is asking for $500
Thank you for any help you are able to provide to me.

Looks like an honest watch but hard to tell if the dial is undamaged and the marks are on the acrylic crystal which could be polished out. The gold plating isn't the most sought after version and the heavy deep tattooing on the back isn't a plus either. At $500 plus paying for a service you will probably end up into it deeper than you would like. Try to look around a bit at other examples.