I am also a platinum menber for a 2 years and made the follwong experiences:
I was recently 2 times in the Crown Plaza in Beijing (booked via PC website, very cheap rate). The first time I was upgraded to a executive room on the club floor, the 2nd time I was upgraded to a suite. But in both cases no complementary breakfast or free access to the club lounge.
I was never upgraded in the US (Holdiday Inn, Express, Staybridge in the Philadelphia area), France (Holiday Inn Aix-en-P.) or the UK (Holidy Inns in London and Runcorn).
I usually get an upgrade in Berlin/Germany (H.I.), but not in Cologne (Crown Plaza).
I always get an upgrade in Prague (H.I.)

Regards

Peter