Haven't used it since my 6 week stint - no intention to. I probably spent 4-5 hours on back and forth (over the course of 7-8 weeks) to get nights and points added - you can evaluate if that's worth it for you. Keep in mind Marriott don't run the experience, you book through them but then it's handed off to a random property agency.
Firstly, if you're trying to get the nights before the end of year it's probably not going to play out well.
Assuming not. If I wanted to be a little more strategic and likely spend the same amount, I would find the same / similar property on Airbnb at likely a 20%+ reduced price (which you can negotiate) and then use the 20%+ saving on either a nearby cost efficient hotel bed or just find time to go away.