This can definitely add up, being 8 City Bucks per spin. There is also an element of randomness, because you are not guaranteed to get a piece of water park that you haven't already received. This can be very frustrating and expensive. However, once you have all of the pieces, the opportunity is there to create a beautiful and large water park in your city.
Have you played the Social City raffle? How many waterpark pieces do you have?