I was talking to someone at United on the phone (switched row on economy plus, for $5 more per seat, and the first upgrade was refunded), and she stated that if I choose to go to First, the economy plus upgrade would be refunded. But yes, that is where my math came from.

We just booked the flight yesterday and will travel in 2 weeks, so there a bit of a premium there. The price on the resort makes up for it.

It does appear that waiting/watching the price might be worth it. I've just never flown above economy plus, and this seemed kind of reasonable for the price. Worst case is, we still have decent legroom (we're both under 5'7" - the only plus of being short).