Air France and KLM will both give you access to "Economy Comfort" seats for free as a Delta Platinum. Unlike Delta, you don't need to wait for an "upgrade" -- just pick them on the seat map after your flight is ticketed (you may be asked to pay during the booking process, but once your flight is ticketed they should show up as free).

Neither Air France or KLM provides complimentary upgrades to a higher cabin in the way that Delta or the other US airlines do. If they oversell Economy and need to upgrade you for operational reasons (search FlyerTalk for OpUp), being Platinum might help but you are still behind airline employees, then Flying Blue elites.

Both airlines have been known to provide inexpensive upgrades at check-in (I was offered a €500 upgrade from Economy to Business on CDG-JFK recently), you may wish to ask an agent or keep an eye on the seat map on airfrance.com / klm.com -- they will show up close to departure as available seats for a fee.

There have been a lot of problems with Amsterdam Airport Schipol recently, which may tip the balance in the favor of a single connection in CDG.