Not true. I've successfully gotten several Priceline-booked Westin rooms upgraded after showing my SPG card. Simply a matter of asking "I don't suppose you have any king rooms available?" and smiling very nicely! (Granted, it's possible I would've been upgraded even without the SPG card.)
Also, FWIW, I received a "free" upgrade to SPG Gold last year after I hit OP Gold level, so this isn't a new promotion.
Originally Posted by iriefrank
SPG won't upgrade you on a Priceline fare. They might give you late checkout, but the rule is no. But definitely they won't bend the rule on upgrades.