When doing ATPL Groundschool (BGS) or any of my flying training I've specifically sought out either the ex military or very experienced instructors. When I chose to do something a little more useful with hour building I did an IMC rating with an instructor who had c 19,000 hours teaching mainly in light aircraft, and CPL/ME/IR wise I found just the man - again very experienced and ex RAF.
Downsides to this approach are a few old school style bollockings but I learnt from those errors
When being taught or instructed by such people the quality and quantity of knowledge seems to occur by osmosis as much as anything else.
So to answer the OP -I think it literally is priceless.