Hi Jean
I did this trip last May and I did not know that you could upgrade for a room with sea view so did not do so. But having said that I had a very big standard room with good views of the swimming pool and the sea from my room window. I met a lady who had a room with the sea view - the rooms were a bit closer to the sea. The sea is very near the hotel - you just walk across a short private bridge. I guess it would be worth upgrading if you mean to spend all your free time in the room, otherwise I personally would not do so. Hope this helps.
By the way you will have a great time as Costa de la Luz is lovely.
Jaya