Ours sails very well on all points of sail. When the breeze comes up it does very well under just jib and mizzen. A dry seaboat that inspires confidence. Under power its fine ahead but going astern is "interesting". Things have improved now we have fitted a kiwi folding prop, not just the sailing capability but also in astern I now know that most times it will kick to port.
I have a Halberdier, which is of a similar style and era. These type of boats do hold their value well as anything more recent of a comparable size offering wheelhouse type layout is very pricey.
The one thing is that I would say is that for this sort of boat at that sort of price the gear should be in good shape with reasonable recent upgrades. Likewise sails/standing/running rigging should be recent. I dont know what the fuel and water tank situ is on a Neptunian but ensure that your surveyor checks these out...its possible that they may be the original steel ones. On the Halb these last about 35 years and are a nightmare to replace (not to say they are on a Nept) Happily mine were done with a pair of shiny new stainless ones when I bought the boat 7 years ago.
Has the hull and deck on the one you are looking at been painted?? Many boats of this age are or now need to be.. check if its 1 or 2 pack paint...brush or spray?
Engine..goes without saying that unless you know about diesels its worth getting an engineer ti look at it especially if its original equipment..what is it..some engines like my Perkins 4107 are cheap and dead easy to work on..my wheel hse floor opens up and I can sit on my engine whilst I work on it..makes it almost a pleasure!
The list goes on and on but if its good and well cared for a motor sailer (wheelhouse cruiser!) is a great boat to own. Ive spent 2 2week hols on my Halb this year in N France and the CIs and its like living at home, and sailing wise I find that I can keep up with all the new boats except when really hard on th wind.
BTW another nice boat from the same period is the Barbary Ketch