Upgrades are possible, not guaranteed. It depends on when you check in and who else is staying there. There could have been a dozen platinum or gold members who checked in before you or others who paid for upgrades. Gold may seen like a high level, but if you follow these posts, there are many out there who stay 100, 200 and even 300 nights/year. As for breakfast, as a gold member, you can get a free breakfast at any hotel in the Marriott chain other than Courtyard.
If you are looking for a room upgrade, those can come in many different flavors, as has previously been noted on several Insider threads. An upgrade or "best available room" does not necessarily mean a suite. Instead, an upgrade could mean a better view, better access to amenities such as the pool, a larger room, a room with a whirlpool tub, etc etc. Moreover, most Courtyards have a limited number of suites. As far as breakfast is concerned, Courtyards do not not include breakfast in room rates other than rates at some Courtyards which specifically are identified as "breakfast included". Note that a number of Marriott brands do include breakfast in all of their room rates.