I'm not going to get into the "should vs shouldn't" argument, but I'll outline my spin background a bit...
When I was a 16-year-old student pilot (you KNOW this paragraph isn't going to turn out well
), my instructor showed me how to do spins in a Cessna 140, and then in a Cessna 150. During my solo flight practice, I spent hours and hours doing spins. Didn't tell my instructor OR my mom. Even got lost once, because winds aloft were kind of strong that day, and blew me 50 miles from home. Foolishness at it's finest? Nope...read on.
When I was in college, we had a homebuilt aircraft. I was circling well outside the 500-ft limit from persons, vehicles, vessels, or structures, looking at something in a field. Got slow, flew through my wake, stalled, and got into an incipient spin. Fortunately, I had enough spin practice to immediately recover, "plenty" of altitude to spare. Sure, a fully-developed spin would have been unrecoverable at this altitude, but I didn't feel the need to let it fully develop prior to initiating recovery.
Ah, but it gets better. I decided I'd better familiarize myself with the spin characteristics of the airplane. I determined that spins were an authorized maneuver in the airplane. I computed a weight and balance with the desired fuel (the tank was ahead of the cockpits, and more than about 1/2 tank resulted in fuel coming out the vent and into my face during stalls, so I wanted to be 1/2 tank or less), and determined that I was within the CG envelope. Barely. The pencil mark didn't quite touch the aft limit. So off I went. 5-6000 ft, slowed it down, stalled, kicked it over (the airplane does the most asthetically pleasing spin entries, IMO), and initiated the recovery after 1/2 turn. About 1/2 turn later, apparently without even slowing the rotation, the spin reversed direction. Quick opposite rudder and then neutralizing it stopped the spin, and I recovered. Idiot that I was, I decided to try that again. And again. And again...same result each time, either direction. Landed at my uncle's airstrip, and noted a pulse rate of something in the neighborhood of 150 bpm. Just a touch stressful, apparently.
My next (first, and only, in fact) flight review, I requested that we do some serious spin training in the 152. I found a CFI who was comfortable with spins, and we had some serious ground and flight training regarding the aerodynamics of spins, spin entries, spin recoveries. We also discussed my experience with the homebuilt...I can't print his comments here, since this is a "family" board, but he was definitely right. I later did an abbreviated review/flight for CFI spin endorsement with this same instructor. Still more in-depth than a lot of CFI spin endorsement flights that I've heard tell of, though.
My initial CFI certificate was in gliders, and I did a short spin flight for that endorsement. One of the primary focuses of that training event was how to keep the student from killing you in the process...being a tandem aircraft, there is a somewhat higher likelihood of the student doing something that you can't stop than in a side-by-side. That's where I learned about the "piano wire" technique. As a glider pilot, btw, inadvertent stalls and incipient spins are common while thermalling (you thermal at minimum airspeeds for small turn radius).
One of my early jobs involved giving aerobatic rides in Stearmans. One of the other pilots spent the better part of a day with me training spins in the airplane, including some more unusual entries and recoveries. Highly entertaining and informative.
The point of all this (you were wondering about that, weren't you?) is that, while I have always been "comfortable" with spins, the initial training I had as a student, which didn't amount to much more than a "watch this" followed by "monkey-see, monkey do" was extremely inadequate from a safety perspective. Fortunately, I was proficient and comfortable enough to deal with the spins I entered both intentionally and inadvertently early on, but my bag of luck got quite a bit lighter by the time I was 20 years old.
IF spin training is done, it needs to be thorough, IMO. "Invulnerabillity" runs pretty deep in pilots, particularly younger ones. Also IMO, besides the motor skills involved, there is a fairly large shortage of training on when spins are appropriate, and when they're not.
If I were to spin-train a CFI, I would make the program as extensive as I could based on my knowledge and experience, and would consider it minimal for the task.
Fly safe!
David