That's the thing that's made me a little divided about The Plan: the reaction seems to be either that it's a great addition for the BSG universe that allows a new spin on events in the series and gives us a better idea of the Cylon perspective, or that it's completely unnecessary filler.
I think I will ultimately watch it, though. Here's the thing: that last line of the old intro of "And they have a plan..." was a hell of a great hook, but you never really had an idea of what that plan was. At least, you never got an idea of what exactly the Cylons had planned. I'd like to think it was something more sophisticated than:
A) Blow the shit out of humanity.
B) Chase the survivors around the universe
C) Conveniently have a few models with the survivors on the ships to cause some MAJOR shit when possible
It may not be entirely satisfying, but still, since I am done with the series, it'll be worth one watch at least before re-watching the series already.