My assumption is that SNAs and complimentary Platinum elite suite upgrades will apply to RC properties (but not Singapore or Reserves) after the August conversion into the new loyalty program.
However, please keep in mind that each hotel assigns the select suites and rooms that are to be included in the upgrade pool. In the case of RC, upgraded rooms and suites will never include Club rooms or Club suites. So you might get upgraded to a better room or even to a suite, but never one with Club privileges. Heck, I was just at the RC Boston where I’d booked an Executive Suite, and I was upgraded to a Luxury Suite—but still without Club access.
Any possible (and likely very rare) upgrade to a Club room or Club suite with Club access would be entirely at the discretion of the hotel and not related to the guaranteed elite benefits.
As for the contrast with St Regis and Luxury Collection, yes—I’ve had tremendous success as an SPG Ambassador level guest getting complimentary Platinum suite upgrades (both with and without SNAs).
The benefit of SPG Ambassador status is that I’m almost always upgraded to a suite (and always to a much better room category in the very rare instance when I don’t get a suite) at any SPG luxury hotels at which I stay. I expect that to continue under the new Marriott Plat Premier with Ambassador service status, as well.
Of course, the biggest reason I love StR and some LC hotels more than RC is entirely due to the butler service that is inherent to all StR properties, with complimentary daily coffee/tea service, complimentary unpacking/packing service, and complimentary limited pressing/shoe shine service.
The breakfast benefit might be nice to most, but if you can afford the StR or RC room rates, chances are good that you’ll be fine paying for breakfast. I prefer room service, so that usually isn’t included in the breakfast benefit at most StR and LC hotels (though even that has been offered in a few less frequent instances).
For those who love lounges/clubs, the RC is certain to be the favorite. I could care less about those. But my husband loves them.