Not sure if this helps the OP.
I have been repeating this as well, W., and it's been my long experience.
But do you think it holds true with overall boat speed, or more to do with the quality of rowing?
or both somehow?
the culture here expects that if you are going to race, it better be in a newer boat, newer=faster. My observation from the masters is that they all believe this is true, they think they're going faster.
One masters woman at our club has been kicking ass at masters racing over the past 4-5 years, and if had gone to a competitive level training plan a few years ago, would be a nat'l team candidate. She insisted that when she bought her new fluid that it made her a lot faster than the beat up ancient Kaschper she'd raced, or the Maas trainer before that.
So I went back and looked up her past results, looked up her erg scores, etc, and learned that when she started at the club, she hadn't trained in rowing since college 7-8 years before, she's stayed in shape but not really training. She's an excellent athlete, a pretty average sculler, and you could see her on water racing exactly track her ergometer improvement as she gradually trained her way into very good fitness.
I've seen evidence of a sculler going faster when swapping one racing hull for another, seemingly where it must mean that the hull he selected must be better. Yet I've seen another sculler jump in his previous hull and beat him in his new one. They were similar athletes (nat'l team), and very average scullers.
The human mental part, and physiological parts of rowing contain such huge variances for an individual, a far bigger spread than the differences between a couple modern hull designs, or the differences between a new and ten year old boat. If the boat is still effectively transfering the power, if the hull is straight and finish good, if the boat weight is within a few pounds, I've yet to figure out what can be "faster" about a new boat.
Newer boats go faster than quality old boats because the rowers believe they will.