This is inaccurate. Grand Seikos fair no worse or better than other luxury watch brands on the secondary market, such as Omega, Breitling, JLC, etc .... with the glaring exceptions being Rolex and Patek. They're in their own special universe on the secondary market, with some AP models there too. Everyone else, more or less, is in the same boat.
Sure, there are exceptions based on models, but 25-30 percent off of retail is more accurate for the secondary market for Grand Seikos, and there are some LE models that retain their retail value very well. I'm in the market for my first Grand Seiko and I've been watching them closely for the last six months or so.
As for the debate about movement finish ...
that would be way down the list of priorities for why to purchase a certain watch. The way the dial and case look on the wrist is THE primary reason guys buy watches, with accuracy and the fit, finish and feel other important criteria. I couldn't care less if internal parts I never see have a beveled edge or not.
Grand Seikos are so beautifully finished (dial, hands, case, and to a certain degree, the movement) and they have such a cool history, that they definitely deserve a look. I'm mostly a vintage Rolex guy, with a couple of others thrown in, but Grand Seikos appeal to me specifically because they are NOT Swiss made. And so much Japanese stuff in general is just cool.