We stayed with 3 FNC + 1 night points the second week the hotel was opened. My advice would depend on whether you plan to go on excursions off site ({national parks, water falls, etc.) vs chill at the resort.

We had planned to have 1-2 adventure days but in the end we stayed at the resort the entire time minus trips offsite for dinner and some shopping. If we could do it over again, instead of planning the adventure days leaving to/from the Waldorf, we wish we had done 1 less night and reallocated those points to staying at the SLH that's at the thermal springs near La Fortuna. (it's much less points if I recall)

Also I would reiterate to not let any of the bad reviews worry you, we had a great time and it was a great use of FNC's. I would never pay cash to stay here but for a certificate I can't see how you can go wrong.