If it was just me, I would consider it.
I am mainly an EPCOT person. If a single park AP was cheap enough I would consider buying it and then a no-expiry 10 day pass to use when the urge to go to another park comes.
However, I have my kids. One is a MK fan, and the other is an AK fan. So when you factor that in - no, a single park AP is not for us.
-dave