Unlisted benefits of platinum membership :
1. Soft landing - if you fail to requalify for platinum or even gold, you will drop only one level to gold in the following year.
2. Multi-year platinum members who fail to requalify (usually 3+ years of platinum membership) will have their account reviewed manually by Marriott to determine if they will keep platinum status for an extra year to encourage them to stay more in the following year. I have actually met people in the CL who have gotten this favor in the past.
3. Late checkout - there have been times in prior years as a platinum member where I asked for a late checkout, got a no and then a wait a minute you are platinum so it is okay. Would this have happened as a gold member? Possibly, but I knew being platinum gave me a higher priority in getting the late checkout.
The difference in treatment is more pronounced with properties in Europe and Asia. You get better upgrades. My personal experience outside the US has only been in the UK, but I definitely saw a benefit to being a platinum member.