After letting my AFI rating lapse some 15 years ago and being currently in the process of revalidating it – effectively I am having to do the whole FI course.
Personally I feel that the standard of teaching on my “second” flying instructor course to be a lot better. I also feel that I am expected to teach to a much higher standard to pass my renewal/revalidation test.
I would therefore assume that the standard of the finished instructor to be higher today than 15 years ago. There is no doubt in my mind that I will be a better instructor this time round.