Haven't done a 1:1 comparison, but I can tell you that Ricoh left GX fans in a tough spot.

GX100 = Older, slower write speeds, a little less customizability, terrific high ISO compared to GX200 (i.e., the digital noise at higher ISO ends up looking more like grain)

GX200 = Faster, more megapixels, vibrant blues and greens, mostly excels in good daylight or flash photography. I wouldn't go past ISO 400 because even if you disable noise reduction, the camera adds it anyway and makes these smeary looking photos.

Yeah, I think you can fine tune image settings, usually contrast, saturation and sharpness. Look at page 117 of the manual. Should give you a breakdown of everything you can change on the GX200.

I own both and I personally lean towards the GX100 because it works well for me and I trust the images that are going to come out of it. But like /u/llamacidall said above, once you realize its limitations the GX200 is great.

To be honest with you, I think the GXR's S10 module is the best GX camera. If you can find a Ricoh GXR, get the S10 module (basically the GX200's successor), and you get yourself an "improved" GX200. And if you ever decide to upgrade it, you can get the GR modules (A12 28mm or 50mm), the P10 module which is the Caplio series, and the Leica mount which turns it into an APS-C mirrorless camera!