In general .. I can't see using Fast Passes for shows (especially at a park that only has 5 rides). If you show up early enough or go to one of the early or late shows, you should be able to easily get a seat.
That being said .. if you have no interest in some of the rides at the park (or going with little kids who aren't tall enough to ride RnR, ToT or Star Tours .. then ... sure .. why not grab a Fast Pass for probably the most popular show at that park and know you can show up shortly before the show starts and get a seat.)
Fast Passes for shows (while not necessary all the time) .. just saves you some time so you don't have to wait 30+ minutes before a show. No different than not having to wait 30+ minutes in a ride queue.
So it all depends on how important that show is to your group.