Although I have much respect for Jeff, I find this statement to be a bit contradictory. If a fiberglass boat has survived for 40-50 years, and the glass work is considered to be not very good, then I wonder what "good" glass work would yield...
I will try to explain where I am coming from. Roughly ten years ago the marine insurance industry sponsored a report testing older hulls. According to the preamble of that report, there had been a consistent number of claims where the damage was in excess of what would have been expected from the impacts involved.
The testing in that report took actual panels out of older boats and examined them in a number of ways. They physically examined the layups. They looked at their strength compared to what their calculated strength should have been and compared them to panels that were laid up for the tests with a similar laminate schedule. There was also chemical testing and laminate to resin ratio testing. They also looked at standard boat building practices of the 1960's and 1970's.
The report concluded that a number of building trends were typical within the industry. The report indicated that the resins of the day were less ductile and so more prone to fatique. That the industry tended to use much higher concentrations of accelerators. The concluded that the way the glass fibers were made made them more brittle and the way the cloth were typically handled at the builders tended to snap individual fibers. The report indicated that resin mixes were not carefully formulated and so varied widely from lay up to lay up within the same section of hull. The report concluded that there was less care in laminating to assure proper resin to fiber ratios. The report indicated that there was a tendancy to use a larger amount of non-directional fabrics (mat or shopped glass, but mostly mat) as thickening method. That boats of that era lacked internal framing which tended to cause greater flexing and higher stress concentrations than the boats which followed. That this greater flexure and lack of ductility resulted in a greater reduction on strength due to fatigue and fiber break down due to work hardening.
When the historic panels were tested they were shown to produce far less strength and stiffness than would have been expected either by calculation and by comparason to the newer test panels fabricated for calibration purposes. The broad conclusion was that the strength of these older hulls were seen as being less reliable.
There is also that myth that these older boats were built stronger than modern boats because the builders did not know how strong fiberglass really was. In talking to pioneers of that era and reading the documents that existed at the time, these early designers knew precisely how strong fiberglass was. The US government and Owings Corning had published all kinds of data that had been developed during WWII. For example, guys like Carl Alberg was designing composite structure for the Military at the time that the Pearson cousins brought him back to yacht design.
In reality, the thicker hulls of the era reflected the known problems of the day achieving uniform strength levels in large laminate structures and the large amount of flexure typical of monocoque or near monocoque fiberglass structures which was typical in early glass boats. The insurance report suggests that these boats were not over-built when viewed over their entire service life.
In my own experience, when I worked in boatyards, it was not all that unusual to cut a hole for a thru-hull of some kind and discover lenses of either resin which was not fully catalyzed, resin rich pockets or resin starved mixtures. But more to the point, over the years I have seen cases where an older boat bounced off a dock once to often sheering the hull just below the deck line. I have seen cases were there are large, deep cracks (20-25% of the laminate depth) radiating out of higher stress areas.
So while these boats still exist, and are probably fine for coastal cruising, my point in saying "built at a time when glass work was just not all that good", is that I seriously question whether over time the older boats will make a good reliable choice for the day in and day out rigours of distance cruising.