I think the best benefit of Plat is the room upgrade although that's not guaranteed (depends on availability). Other benefits include guaranteed room availability (72 hours in advance) and also a 50% bonus in base points, which I also find invaluable in renewing my status.

The thread below has a lot of posts where you can compare notes on how other Plats have fared with regards to upgrades:

http://www.flyertalk.com/forum/inter...periences.html