Its a nice thread you have started & almost all the points you have mentioned I have dealt with over the years & tried to fix myself so seems to match common experience. The problem with ASCs or mechanics is that they are just there to make their income & don't try too hard to properly investigate & fix the problem or for that matter save the customer's money. Most of the time its change this part change that part or just change your CAR!
One point which I don't see & is probably the most common in Cars with lot of mileage is at some point the heat sensors stopping to work leading to the cooling fans stopping working and coolant boilout & such issues. If this happens one should know that there is also sometone called an "automobile electrician" who can fix your problem. Going to mechanic will only result in him wasting your time & probably money as well.
The other thing I wanted to add is SPARE PARTS!
Please INSIST only on good & genuine spares like MICO & manufacturer genuine parts!
I have had so many repeated trivial complaints in so many areas due to cheap local spares. The spare part shops will typically call it "Delhi make" parts or duplicate parts.
One more thing for people buying brand new cars to consider is how long they stick to ASCs & whats their strategy because you want to maintain your car well but most people realize that it has to be done at an optimal cost.
1. Some people just take basic default warranty & just go to ASC for the free services.
2. Some people like to stick to ASCs for longer period & go for extended warranty etc.
3. Some people know that extended warranty is just a way of making money for them & skip it.
4. Some people start maintaining the car themselves with help of reliable mechanics immediately after warranty expires.
5. Others still do a mix & match of taking simple issues to local mechanics & more complex issues to ASCs etc.
Again like the original post says there are so many departments within a car like mechanical,electrical,HVAC,interior, bodyshop that you really have to be really a auto enthusiast yourself to try & maintain it well yourself OR just shell out the money & get someone to do it.