It depends upon how much risk you are willing to take.
None of my current vehicles carry collision insurance. If one of us is in an accident that is our fault, we bear the costs of replacing/repairing our vehicle and are prepared to do so. My person guideline is a vehicle value of somewhere around $14,000. A value more than that and it is worthwhile to carry collision. Below that and it is cost effective for us to self-insure. Needless to say we carry full liability and medical (maxed out), as well as uninsured/underinsured motorist coverage. We're assuming that an accident will not be our fault, and if it is our fault we will bear the costs of repairing/replacing our vehicles.
I keep more than enough in our "vehicle savings account" to pay for a replacement vehicle should any of our current vehicles be damaged or totaled in an accident. That account is made up of not only the monthly payments we make to ourselves, but the savings from not having collision insurance. About once a year I take the excess and put it into a higher yielding investment and let the principle of the savings account continue to grow as we add to it by making vehicle payments to ourselves. The longer I keep vehicles and maintain an accident free status, the more the account grows.
In 2-3 years we will probably replace my wife's Subaru, and assuming we purchase her a new/almost new car it will have collision until the value reaches a point that (for us) is worth the risk to self insure the collision portion of our vehicle insurance. I can't peer into the future, so I do not know what that figure will be. I'll run the numbers at that time and factor in what makes the most sense for our situation at that time.
Keep in mind that we haven't had a ticket nor an accident in around 40 years. For our 4 vehicles we pay less than $1,000/year in insurance premiums.
It pays to be a cautious driver.