Room upgrades are a mirage. Don't expect to get any until you're at least Platinum for Marriott...and even then, don't expect any. My batting average is about 30% for upgrades as a Platinum. Don't get me wrong, I certainly appreciate them when they happen, and I had one this year where I got the presidential suite at the hotel during a conference, which was VERY nice, but they're not "guaranteed", nor are any of the benefits at Marriott.

4pm checkout, followed by breakfast are the two best benefits to me from Marriott Plat. Like all things Marriott, the hotels don't always follow the rules, so expect that you'll have to fight for it at times.