There are plenty of GS that hold their value well. For all the hype about the SS sports watch grey market people forget that one can buy new DJs and Calatravas at discounts (and big ones on Cellini). I love my OP39 and “Spring” equally but the GS is far better finished.I think with most modern Rolexes at +/-2.0 seconds, the timekeeping is not much of an issue. One can always get better time with a spring drive movement but so far Grand Seiko is not keeping up with Rolex in resale value.
That said, I would love to have a Grand Seiko because I love the finishing of them and I do think they are a bargain for quality.
Rolex and PP are more about speculation than horology these days (and Rolex makes 200,000 watches less than they used to). Rather unfortunate.