We just got back from a 5 day visit. We are one of the DVC member, go at least once or twice a year, have an annual pass type of visitors. We actually only got fast passes about four times during our entire trip. Once we got passes that we knew we couldn't use, because they were for TSM, and they were for the hour right before closing, and we had dinner plans elsewhere.
So, I would definitely not pay extra for more fast passes, unless you could really choose the time of the fast passes. But, I am OK with not going on TSM on any given trip (or Space Mountain, Soaring, test tract, etc), when I am there at 10 am, and the fast pass is for between 9pm and 10pm, because I already have another trip planed in December, and we are going to go next June, before these annual passes expire.
I would only pay extra for a fast pass that didn't have a time constraint on it.