No, I guess we weren't. I was thinking you were meaning normal observation, and my own experience with "inspections" in the USMC. (Very perfunctory, usually.)
But, let me be more clear: A good/professional disguise is supposed to pass normal inspection. Even the TSA screeners don't go "all-out" for every peeson that comes through, they get bored and it becomes monotonous, so they do not (cannot many neurologists would say) stay fully focused and go on "auto-pilot" much of the time. Only when something - usually subconcious on their part - doesn't jive with their inspection-program do they come back to full awareness and begin to really inspect. Heck, the most intense scrutiny I have ever had going through security at an airport was in China, and it still took all of 2-3 seconds for the security individual to check out me and my passport, stamp it and let me pass. Everything seemed in order (and was), so no subconcious cues were triggered to make them suspicious (other than the normal level of suspicion of a westerner) and, poof off I went to my next destination. Now, one can make the argument that those aren't true inspections, and I don't think I would completely disagree, but it is in their job description to "inspect" everything that goes through. I just think you are not including the human factor in the word, and how it is implemented.
It is the quick, just not looking like yourself type of disguise that will have next to no chance of surviving an inspection.
But, back on-topic: I still think that an RR is in order, eventhough I would rather limit the number of rolls during a game, it seems only fair to give the invisible person a chance. But, something to consider: is the tracking spell affecting the individual or the area the individual passed through? If it is the individual, do they get an RR as it stands now? Because they should, shouldn't they? If it affects the area, which would bypass an RR
Instead of all that, how about the Ranger makes a spell-casting roll and the success determines if it is able to pierce the invisibilty spell? A normal success doesn't, but an Absolute and/or Unusuall Success does. One roll to rule them all..... The invisibilty might, or might not modify the spell-casting check, but if you are already calling for an Absolute or higher success, then it probably shouldn't.