Just get the Ritz card and spend 75K a year and you will have Platinum every year.
75K on the MR card with the 15 night bonus would give you 40 nights credit towards status, that also counts towards lifetime totals. The Ritz card doesn't give you night credit, just status, right? If you also have 35 nights/yr from stays or roll over that gets you to platinum. Might work better depending on your individual situation.