Some really good points have been raised here.
From my instructing experience I found it always helped, being able to adjust my attitude to each student who you sit next to.
Constructive critisism worked well with the businessman when I asked him to, "Maintain the centreline please." But when I flew with the local motor mechanic, things along the lines of "Are we landing on grass left today?" worked quite well. Always depended on the style of the customer of course and always in their interest.
Victa I think you identified "Instructor burnout" when you said you were'nt enjoying teaching as before.
Stop "instructing" for a wee while and I always found you bounce back with a vengeance.
Cheers
GA Driver