Re: Opinions on 3D graphics in porn
It's a poorly phrased question, really. Whether or not something looks good isn't a direct function of the 'era' of the graphics. Just backing out of the H-games thing, compare and contrast, say, SSBM and God of War (original release). SSBM still looks pretty good today, whereas God of War looks much more dated, even though SSBM is the older game. Most of this comes down to the fact that SSBM's art style didn't need huge processing power, whereas you could argue that God of War required more than the PS2 could provide (I believe that game had some frame rate issues...)
More modernly, you've got pixel art games which you could argue have SNES-era graphics, but they look great. Kickstarter provides a huge number of examples of this (e.g. Timespinner, Hyper Light Drifter). There's other games as well, which despite low poly counts, still look pretty damn good (Massive Chalice).
So where's this going? Basically, Art style needs to complement the choice of medium. The more realistic you get, the more resources you'll need to put into the art. But if you go more stylised, then I don't see having a lower-era of graphics as a problem.
One word of warning though: the majority of PS1-era games that used 3D were ugly. There's a reason why there was a lot of pre-rendered backgrounds on the PS1 - it just couldn't cope with that number of polygons without them being incredibly low detail. So unless you've got a way of coping with that kind of restriction, I'd say that Dreamcast-era is the minimum required for a 'typical' art style.
I'd also note that Dreamcast-era is the first instance of Cel-shading, which is technically low-poly (the models used in Jet Set Radio aren't particularly complex, but the shaders are). That might be an interesting route to go down if you want low-poly stuff.