You've gotten several good responses telling you how you can make Platinum before year's end but not really saying if Platinum is worth it or not.

If you are going to be staying in full-service (Marriott, JW Marriott or Renaissance) properties most of the time and if you are going to be a frequent enough stayer that would sustain the Platinum level, then the answer is "yes"! The Platinum perks make a difference at these properties.

If you are going to be staying mostly at limited-service properties then going out of your way to attain Platinum status is, in my opinion, not worth it. In this case, I would agree with bigguy and direct my efforts at making mid-tier status in another chain so you would have a fallback when Marriott's weren't convenient or available.