Lots of good options above. If going for another card and doing it completely free isn't feasible, I'd spend $10,000 on the existing SPG card yielding 30,000 MR completing the 5 night deal and paying $220 for night 6.
Also if the entire 6 days is available at $220 and future travel is in your medium range plans (before too many devaluations), I'd pay cash and save the points for another more expensive property. Cat 9 is tops anywhere in the world! (just not RC's).
Or a travel package.