I just finished a few stays in Hawaii and here are the platinum alternatives that I received:

Sheraton Keauhou Bay - complimentary valet parking (instead of $6 a day)
Sheraton Princess Kaiulani - Coupon for platinum happy hour (choice of three of their $5 happy hour appetizers - edamane, fries or meatballs)
Westin Moana Surfrider - One breakfast coupon per day

I was only at the Princess K for one night so I am not sure if you receive one happy hour coupon per day. I thought people were exagerrating about the Princess K, they were not. Staff is friendly though.