I see you have come around quite a bit in your thoughts on this. Congratulations! However; let me assure you that such instructional flying by a senior pilot would not be a waste of anyone's time. Most young instructors just don't understand fundamentals of flight, in particular just what the rudder is for and how to properly takeoff or land in a crosswind, among many other important things. Those are the things that are taught much better by an experienced, yet expired, CFI than a "green" youngster CFI with 500 hours who hasn't really figured it out yet.
I ran into a young CFI one time who insisted that he knew it all because he had 1,000 TT. I explained to him just what 1,000 hours TT means. Are you ready, remember this: 1,000 hours means that that person is interested in aviation. When you have 1,000 hours in jets, you are interested in jets, and so on. Remember this quote as it will serve you and othes well in discussions with young people because one day they'll find to to be so true. 1,000 hours TT is really very little and can be obtained from scratch in as little as one year and certainly in two years.
While I realize that you and many others have enough flight time to show that they are well past the "interested" stage, I'm surprised at the resistance to an expired CFI teaching, as if only current CFI's know anything. Sorry, but most often it is just the opposite. No, its not the flight time that will count for anything to the FAA, but in learning, it can many times be logged in a special place as the best instruction ever received.