You'll also have exposure to the $2,500 deductible while driving your own vehicle, which is more often than driving a rental. I think you need to have the insurer price various deductible levels to see if the premium savings warrants the higher exposure. The effect on rental car claims would seem to be a minor consideration because you can buy a card with primary CDW for $95/year.
Absolutely. The decision on your own auto policy deductibles should be based primarily on factors unrelated to car rentals. Still, the more cars you rent (and with free CDW coverage via Amex Plat or another card), the more it cuts in favor of having a high deductible on your personal auto policy.