The idea of knocking a course from consideration for slow play is hard for me because it's so random. I guess there are some course designs where play tends to back up, and some venues that overbook every day they can, so that the slowness is really a phenomenon. But it's just as likely to be a day where you were unlucky, had a late tee time, and were stuck behind some bad golfers.
However, I would be okay with people including the "experience" as a part of their rating, if everyone did it consistently. In that case, a one-time bad experience wouldn't have nearly the effect of a course which was consistently slow.
I got onto this idea when considering weather as a factor in the rankings. No one ever really addresses that, either, but there are a few courses where the weather is a factor so often, that being told to disregard it is disingenuous. Indeed, on a course in a windy place, a design that allows players to get around in the wind and still enjoy themselves should be a major consideration as to whether the course is really good.
You could do the same for conditioning -- as long as everyone did it consistently, then the bad days would be scored at the proper rate.