Yes it appears that upgrades don't come often at the SJ Marriott... I've been staying there a lot lately for work trips and only gotten a real room upgrade twice out of 8 stays... one was to a "CL level room" which had improved room amenities and also in range of the free lounge wi-fi, and the other to a larger corner room. The rest were normal rooms on upper floors which were still pretty nice. That was as a gold, now as a plat I will have to see if I have any better luck.
CL breakfast is noramlly nice, and the evening attendant is wonderful... plus the icecream and snacks are great.
I've found that the front desk staff is not very willing to provide room upgrades even when there are plenty available as other people have noted in this thread.