There are numerous threads about the (designated and soft) benefits of the Platinum program.
Some - like me - see very good value in it for my rental needs.
Others are not so certain.
One of a number of representative
threads on this topic.
My advice would be to keep your expectations in check with regard to Platinum upgrades.
Both Prestige and DREAM Collection vehicles are beyond the scope of the program.
That is not to say you may not be upgraded to a Prestige vehicle.
But do not expect to rent a compact and drive off gratis in a Porsche or a Range Rover. That is simply not going to happen.
Yes, there are nice upgrades. But I've also had no upgrades at CLT and RDU.
The four-hour grace period at the end of a rental is a very good benefit.
HLE locations usually have a limited selection of vehicles.
Also, it helps to have a relationship with a location manager(s) if you are going to be renting regularly.