Depends when you are going. Last year we went beginning June and found that because of the longer opening hours due to the Dreams Show, that being in the parks from 8.00 in the morning till 10.30 or 11 at night was a bit much. We would go in for extra magic hours, leave about lunch time, come back to hotel and have a swim and a nap before going aout again late afternoon, early evening for more rides and watch Dreams. In that situation having the pool to break up the day was fantastic.
If you are not going to build pool time into your day, I would keep the extra money for meals and treats!