I think FP for this ride are great. I've seen some really long lines, especially in the evening, especially if they take trains off. It's odd, I've seen situations where they had four trains running in the afternoon, no line, and then for whatever reason around 8 PM or so, they take a couple of trains off and only load one side of the platform. Whammo, instant mega 45+ minute lines as everyone comes to ride the coaster in the dark.
In this situation, I'll grab FP, head over to something else, like Indy, HM, POTC, even Tarzan or Pooh, and after a couple of rides there, we're ready to BMTRR. It's not uncommon for us to immediately grab another set of FP whenever we ride, as the return times are always good. If it's disconnected, that'll make this strategy a no brainer.
I do think there's some wisdom to disconnecting the FP rides that don't sell out of FP on a regular basis. If they don't sell out of FP, then there isn't all that much demand for FP, and disconnecting them should allow more guests to use FP on those rides.