I would nominate Castello di Amorosa as the most over the top winery in Napa Valley. If you think winery tours are all the same, then try a day at this castle. It may look like it has ancient roots, but really it was designed and opened within the last ten years. The owners of Castello di Amorosa obviously wanted to simply show off.
Besides being the most family friendly winery tour, as you walk through the castle, they have a non-alcholic package where you are served grape juice and chocolate, and there are even animals roaming the grounds, the tour guide was also so impressive. She gave a thorough break down of how wine is made and was funny and entertaining as well. This is one of my top recommendations while visiting wine country.