Plenty
I've had plenty of "gold" upgrades at SPG properties. I've been platinum for each of the past three years, was downgraded to gold this year because I just wasn't travelling as much last year, and will be platinum again next week (way too much travelling this year). I find that the "gold" upgrades are best at properties that I have stayed at frequently over the past few years and current years. For example (all as Gold):
Sheraton Greensboro: Often upgraded to their "presidential suite" (they have like 500 of these standard rooms with brass fixtures), but still an upgrade w/ club access, etc.
Sheraton Greensboro: Occasionally upgraded to their true suites (at least 2 or 3 times) generally on shorter stays.
Sheraton Austin: Upgraded 100% of the time to the club floor--never upgraded to any special rooms.
Additionally, I've been upgraded this year during a few point stays:
Sheraton Moorea (French Polynesia): Garden Bungalow to overwater bungalow (this one took some talking/complaining though, but it was my honeymoon, so well worth it).
Westin LAX: Club floor (no special room).
As a Platinum previously and now a Gold, I quite frankly do not see significant differences in the upgrades, with the exception of occasionally getting some of the nicer suites (especially at resort/luxury collection properties). But truthfully, at the hotels that just have a club floor with few special rooms, the differences seem to be moot.