I realized it's possible to do a lot better.
Suppose meetings are $100 each (for simple arithmetic). Get a Marriott credit card; that's 15 nights/year.
2016, in January: hold 12 meetings ($1200). Be Platinum for the remainder of 2016 and all of 2017, roll over 60 nights, add the credit card nights, and be Platinum for all of 2018. Repeat in 2019. So for $1200 you get 3 years (minus a few weeks) of Platinum status, and that's without figuring in any actual stays or anything else.
Is United Silver worth $400/year? (Or less, if you find cheaper meetings?)