The Marriott employees, that's my experience, treat you really very well when you are Platinum, even if you don't pay the full rate, only a 50% rate of a company code or even on a reward stay.
I think also the difference of being nice depends on the General Manager and each employee. The GM in the Atlanta Northwest Marriott calls every Platinum every week in the room to say thank you !
What Marriott could do additionally as a benefit for Platinum:
- Free Internet Access in (full) Marriott
- Free Beer and Wine in Concierge Lounge (in general or vouchers per day)
- Room Selection ("Which room can we offer you in our hotel?" would be nice)
- Early check-in like the existing late check-out