Yes, a cash booking will definitely cost you more, especially since the Poly rarely offers discounts and when they do, they are nominal. Depending on who or where you rent from, it can be 50% less. Of course, there are a lot more risks involved in renting points, main one is that it's not refundable and dates can't usually be changed. Some companies will allow a credit, but not a refund.
Trip insurance is a possibility, if you can find the right coverage. I would not count on the new tower and a 2BR. Not saying it's impossible, but no one even knows for sure if it will be the same association, which could determine how easy it would be to rent points (if same association, more people with Poly points to rent out).