I argue otherwise. Engine monitoring systems are a nice to have, and very handy for diagnosing some engine problems in very rare occasions.
Most problems most of the timeDiagnosing engine problems is great, if you get it early, and if you're in time to fix early.
Yep, and you get a chance at early rather than at the worst possible time without For that, I support their use - if the pilot knows what they are looking at.
Ahh yes we do agree, time for an APS class for all of them! But if that problem has already shown symptoms in flight, you're also having to deal with it and fly the plane, perhaps as an inflight emergency.
And knowing exactly what the likely problem is will help you make the right call I have certainly flown with pilots of abnormally well instrumented aircraft, who were paying so much attention to the indications, that they forgot to fly the plane - and what they were seeing was really of little benefit to them anyway by that point.
Because they believe the instrument will do it all for them, they need EDUCATION. The rest of your observation is 100% correct
All certified aircraft have engine operating instructions - just follow them!
No, not always and I can show you some that are very poor or bad Keep the engine properly maintained,
YEP and serviced with the proper liquids,
YEP operate it as instructed by the manual, and it will run.
And some will run a lot longer if you do not follow that manual, the secret is knowing which is full of BS The few pennys you might save by extreme leaning
Extreme?? engines stop and other tactics are lost on a carburetted engine, because as Big Pistons correctly points out,
Incorrectly points out no carburetted engine has fuel flow even enough to each cylinder to run "properly" leaned - that's just the way it is,
Not True and you the pilot cannot change that
Yes you can, some more so than others, so just pay for the fuel, and fly the plane. The only way a scanner
a what? can help with leaning is to assure that you are leaning to the leanest cylinder when reading the indication
bad advice, and allowing you to find a power setting which has a more equal fuel distribution than other power settings,
you are now going from stone cold to luke warm... so your leaning is more meaningful. In reality, however, the generic "lean 'till first rough, then enrichen to smooth again" instruction works about as well as watching a scanner for 10 minutes while fooling with the mixture.
It might in some but how would you know? And 10 minutes....geez you just proved my point. If it takes that long to lean an engine how long does it take for a pre-flight? You can do two complete GAMI Lean tets for injector tuning in that time. I lean and set up in under a minute, maybe 30 seconds at any level from 1000' up into the FL's
I have installed scanners for certification flight testing, where data collection well beyond the scope of any GA pilot was required. Two were for detonation testing - that's a whole other discussion, other than to say that if you operate as instructed, you will not detonate the engine.
Never read a Piper Chieftan manual then huh? Incorrect leaning of an otherwise properly operated engine can cause damage, but not because detonation is a factor in that damage.
Ohhh, how so? I do want to hear about this? How exactly did you do detonation testing in flight, with which engine and what data collection probes? I am genuinely interested. Incorrect leaning does cause longevity issues over a long period of time, not just in a 2 minute abuse period. Temperature and cylinder pressures are the things. And these are a result of incorrect leaning. The truth is if you are on the Lean side of Peak EGT you are less likely to do damage by getting wrong, than you are on the Rich side. So the point here is if you operate ROP which is a perfectly valid method for some ops, make sure you do it right. On the lean side there is far more margin for error, except at very high powers such as 1000' WOT and full bore RPM. If you are smart with numbers you can still do this just with fuel flow alone on a conforming engine.
Both my planes do have multi cylinder scanners (left over from testing), and both are carburetted. All the scanners tell me is that I don't really need them 99.95% of the time! I do not peak, or lean of peak lean, as both engines prohibit it (same logic as not over speeding or over stressing it).
You are kidding me...which engines are these? You do realise the big radials of Connie and DC6 days had a TBO some 4-5 times longer when run LOP FACT not folk lore! LOP has lower stress on EVERY engine, where do all the you beaut modern diesels run? 
Their only real benefit is that you can log a changing trend - if you notice in time, and you can identify which cylinder is sticking an exhaust valve or fouling a plug, in real time, and that's informative on the very rare occasion it happens. Though if you stick a valve, and have only that cylinder repaired, you're fooling yourself
Not true at all(and your family may thing you not vigilant!). Other than that, the operating instructions for the engine describe what you need to know to operate it the way it was approved. What else were you thinking to do?
My guidance is not blind in saying the forgoing, as I am delegated to certify the designs of these engines, including detonation testing. I write operating and maintenance manual supplements. The first thing we look for are safe operating margins, and instructions, which if followed, keep the engine well within those margins. People choose a certified aircraft [and engine] for the security of knowing it has been thoroughly tested. It has, so operate it the way is supposed to be. I am unaware that any aircraft has been certified as requiring an engine scanner as a part of it's type design - because they are not really needed!
If someone wants to install one, by all means. Don't let it distract you from the safe operation of the aircraft. Use it to follow (not circumvent) the engine manufacturer's operating instructions. And learn to use it properly. Most flying schools probably struggle to employ instructors who are conversant with the different scanner types, their relevance, and their correct operation. And students hardly want to spend an extra 5 hours of flight training costs to learn what it is telling them, and the relevance.
My family appreciates that I keep myself current and recent,
Excellent!! As we all should and that I operate the aircraft legally, safely, and in accordance with it's instructions. More than that, they do not ask of me....