Using the camera's "auto" mode really doesn't let you compare the cameras so much as their auto modes. As noted, the Ricoh tends to default to f4 when you give it a chance, whether in auto mode or P mode. The grain may just be the NR settings the jpeg engines are choosing as defaults in auto - Ricoh tends to use less NR, which for many is a good thing, but probably not for auto shooters. And its also using the highest ISO, but 1100 is not a challenge for this camera, so I don't think the ISO explains it... But, yes, the Ricoh does have a different color signature than the other cameras, which have a bit more "pop". People will argue all day about which is more accurate, but the bottom line is if you LIKE one more than the other, that matters. It matters less in raw, but it still matters there, because one may give you a starting point closer to your ideal, and require less work to get the final image where you want it.
Don't worry - one of these will likely emerge for you as the one you're just more comfortable with. I didn't know you were a D800 shooter, but that might give the Nikon a bit of an edge, since the interface, while notably scaled back, is conceptually similar to the Nikon DSLR interface. For me, the bulk of my preference for the Nikon came down to the auto ISO setup, which makes my life a lot easier when I'm street shooting - I do a lot of street and this will be my primary (almost only) street camera. That feature probably wouldn't be a big deal at all to a lot of folks, but for me it's huge. I also liked some other less important things better about the Nikon (exposure comp, metering, and I actually came to prefer the simpler interface rather than the more customizable one of the Ricoh, which I've liked a lot for a few years now with other Ricohs). But I also liked a few things better about the Ricoh - snap focus and being able to switch to it immediately is an awfully nice shortcut to zone focus, which I use a LOT, and I've never had a small camera feel better or more natural in my hand than the GRD3 or the GR. The ND filter isn't a bad thing to have either. But on balance, I just started feeling more comfortable over all with the Nikon and the auto-ISO was the determinative reason. You'll probably find one just speaks to you more too. Neither is an even remotely bad choice, but one might be better for you...
-Ray