A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,417
SPG Gold doesn't include room upgrades as a published benefit. You are only entitled to an enhanced room in the same category as what was booked.
OTOH you do get a choice of a welcome amenity, IIRC something like 250 points or a free drink.
Unfortunately (for Plats) Marriott Gold is almost the same as Marriott Plat which is the same as Marriott Platinum Premier, except that many hotels don't even know what PP means and try to insist that it's lower than Plat.