I have booked the REAS for DW and I on our anniversary cruise in late November. I was able to call and already have my reservations for Palo and the Spa, and have had them for nearly a month.
As for a monetary benefit, I think it works out to saving you about $50-75 (not sure of exact figure) over items purchased separately (Palo, Spa, gift basket). You also have the advantage of the romantic turndown on one night and an expanded menu for the breakfast in bed (my understanding is that the normal room service breakfast is only continental items, not hot foods).
Now, DW and I don't have to worry about the reservation scramble, and this allows me to surprise her with the perks for our anniversary (she has no clue).
P.S. I would definitely still arrive the night before. You never know what is going to happen with the weather and/or flights. We are driving down and will still be arriving on Saturday.