maybe yes, maybe no as your plat "entitlement" is stated, as follows:

For Platinum Elite members the best way is up! So every time you check in, we'll do our best to upgrade you to a premium room - at no additional charge – for your entire stay. Upgrades may include rooms with desirable views, rooms on high floors, corner rooms, rooms with special amenities, rooms on Executive Floors, or suites, subject to availability identified by each hotel.

https://www.marriott.com/rewards/mem...ts/platinum.mi

the usage of additional points/cash just "guarantees" your upgrade.....