Your mileage will vary for join-spouse (when both are pilots). In my experiences, if both fly the same aircraft, your odds increase drastically. However, even that is no guarantee. In the end, AFPC does not care about you or your spouse and whether or not you are stationed together. If you are fortunate enough to have a commander that goes to bat for you, awesome. So far, I have not seen any join-spouse members get the "hook-up" when it comes to using it to get the awesome assignments. If both are mobility pilots, don't expect to do a join-spouse in any white jets other than at a UPT base (ie; no C-21s for you).
Don't let anyone blow smoke up your a** about how join-spouse is a priority. In the end, it's needs of the Air Force. Sure, you'll get examples about how that one guy knew that one couple that got the sweet gig...well, they probably had a Commander that went to bat. I'd bet AFPC didn't come up with it on their own.