I read the inspection blog/post a long time ago (was going to say 10+ years, but see it was written in 2009. So at least 5-6 years ago). My rails were silver and I though "Oh no! I'm screwed". That was around the time I started shooting considerably more (1996 p229 bought new in 1996) and there has been no change in the rails. Granted, a lot of shooting for me would be 1-2000 rds/year (and lots of folks shoot that in a month)
I did switch to grease from oil after reading that, not sure if made a difference.
I can't imagine that anodizing will remain on the rails with extended round counts, I'd love to see pics of guns with a few thousand rounds and shiny black anodizing.
Sooo, I personally wouldn't worry much about the rails. All the other points are really good. Of course, if you DID find a used SIG with perfectly black rails I would take that as a very good sign.