I have not seen one of these boats in many years, but this is a design that I always admired. As noted in the ad, the Yankee Dolphin began life in the 1960's as a MORC (Midget Ocean Racing)rule race boat. They were designed by Sparkman and Stephens at a time when S&S was about as good a designer as you could find. The MORC rule of that era produced designs which were also about as good as they got, at least during that period.
Compared to other designs from that era, boats like Dolphin went upwind very well, performed well on a run with the board up, and were good sailing boats pretty much on any point of sail. By intent, these were also surprisingly seaworthy designs for their size. MStern is right that light air performance would not be great.
Boats of this era were designed for huge 170-180% genoas and large full sholdered spinnakers
. Without these big sails, light air performance is not very good. While light air sailing ability is important on the Chesapeake, and I don't know how you sail, many, if not most daysailors and overnighters, chose not to sail in the lower wind ranges, so this may have minimal effect on you personally.
The shortcoming of the rig
proportion is that it requires a proper choice of headsails for the conditions. The large headsails needed for the lighter end of the wind range are way over-powered at the high end of the wind range to the point that you can't simply rely on a furler
to deal with shortening sail and expect to handle really strong winds.
A decent modern design would be expected to offer much better speed, (a PHRF of 265 is approaching the painfully slow category) and better light air performance, but certainly would not get into the shallow water that these boats can slip into.
My recollection of these boats is that they had a surprisingly complete interior for a boat of this size and era. While not luxurious as some of the later condo style designs, I seem to recall a very workable layout for the kinds of cruising one might do on the Chesapeake.
Over time these boats were built by several companies and build quality and details varied, but my recollection is that these boats were simply but nicely constructed. As noted, one of the big "if's" will the deck coring which depending on the particular company that built the boat (and my memory), was either masonite or plywood, neither of which are particularly good cores from a core rot standpoint.
Lunch over, I need to get back to work....