AP increases weapon dps as a factor of 14 AP to 1 dps. Since we have around 3x the usual weapon damage (thanks to the 409 items), AP is worth around 30% of it's previous value, perhaps less because it has that little of an impact. Gemming haste/crit on the other hand (since stuff like Improved Ambush were removed with 5.0) Have a much more inflated value (they were 30% stronger at 80 than 85 in 4.3, which was enough to warrant matching sockets), so you will want to go for more of them.
As for PvP power, it's simply a crit-esque stat (i.e. increases your damage by X%, much like crit averages out to for a lot of classes), and because we don't have any on gear at 80, it's worth using in blue slots.