Given that the American Express platinum card provides for

•One-car-class upgrade whenever possible
•Guaranteed vehicle availability
•Up to a 4-hour grace period when returning the vehicle; complimentary one way rentals, and courtesy pick-up/delivery of vehicle

I am not sure what benefit there would be in spending 2500 points to renew 5 star status. if renting less than 7 times in a year, save the 4 days of rental points for rentals