After careful study, it has occured to me that Darkvision and Scent should not be rated. Both of these are far too insignificant to have any real impact on CR. For Darkvision, damn near everything has it, and those that don't can easily find a light source. (Remember, Darkvision only goes through *natural* darkness.) So standard Darkvision is akin to having a bullseye lantern that only helps you. Also, it is a very low level spell that can also be made permanent. All signs point to Darkvision not being worth anything. As for Scent, I'm not sure why this paltry ability was ever counted in the first place. It doesn't do anything other than alert you to the presence of things that have a smell within a certain range. It doesn't even pinpoint locations, making it useless against invisibility and the like. This ability is nothing more than a duplicate of Low-Light Vision for the sense of smell, seeing as Scent is nothing more than an enhanced sense of smell. Again, it does not impact CR in the least. On the same token, those with Light Sensitivity should not have a reduced CR either, seeing as this vulnerability is very limited in scope and has never once had an impact on any encounter that I am aware of, even after years of gaming. This is just an always active Flare effect, nothing more.
Anyway, I'm certain there are likely other paltry abilities. The stirge's Attach ability also counts as having no impact on CR, seeing as it makes the thing very vulnerable and the blood drain is already counted seperate. Again, there are others I'm sure. I can post more as they come to mind.