So, considering all this
and the benefits of paying less than X $ damage amounts out of pocket yourself,
at what time period ( or vehicle resale value) should all collision coverage be dropped?
When a new vehicle is 3 years old, 5, 7 etc?
Depends upon the value of the car. Remember, you're insuring against total losses as well, not just repairable damage. Also, it depends upon how much you are paying. For example, I paid $3,800 for a very clean, low mileage 2006 Civic for my 16 year old daughter to drive. I could probably sell it for $4,500-$4,800. It cost me $400/year to add her and the car to my insurance. Comp/collision are about $180 of that amount. For me, it's worth the $180/year to keep comp/collision on a car primarily driven by a 16 year old.
My wife's 2013 Subaru got smashed in the side in January 2019. Did $8,800 in damage. We turned that in to our insurance company without hesitation.
