I prepared so much to have one with my first baby. My Drs office used to do them at 30 weeks along, optional, for a fee. I drank tons of water, the scan was amazing, but it was my first baby and new and exciting to me. I tried to have one with my second baby, but he would not cooperate, and I got nothing out of it. This time, I had to redo my anomaly scan at 12+5, and the tech surprised me by switching the machine to 3D/4D for a quick face shot. So I have an amazing picture of my baby's face! I didn't do any of the preparations for it, the extra water and drinking orange juice and all the other tips they gave me the other times, and it was just perfect!!
I would never pay for another one, but that was a wonderful surprise. I do not think it is worth the money, personally, but many people do!