I dont know if people know this or not, but even tho +parry gear initiates more parries, it increases your skill cap which can, at times, put you outside of the skill up range for the specific mob you are fighting. Its just like with PLD, my shield skill ups were coming along just fine, and then I got my AF boots (+10 shield skill wewt!) but after that, my skill ups slowed down quite a bit. Once I removed them and brought my skill down back to its natural level, skill ups came back like I used to get them.
As far as parry is concerned, Id say remove all your eva gear and increase the agi to produce more parries w/o messing with your natural parry skill. Its worked fine for me so far on my NIN