EWR-BCN was ~$2,000 all-in this past summer for PAID, CONFIRMED BusinessFirst. With the double-daily flights it was not difficult to find availability. In fact both my flights were roughly half-empty in BusinessFirst, including nonrevs. I could have also booked a free BF reward ticket, though those seats didn't open up until 2-3 months beforehand. I'm not sure if they'll continue with 2x service next summer.

Sounds like the upgrade will cost about the same in cash, PLUS the miles. While there's no guarantee that CO will have a summer BF fare sale, and if they do, what the prices will be, but it's unlikely to be meaningfully more than the cost of purchasing a coach ticket and paying the upgrade fee.

I would wait.