3.2 Reforging
Expertise and Hit are threat stats with 4.3. They have almost zero survival value. But missing a string of DS in a row, especially at the beginning of a fight, can be quite hurtful.
Generally it's not worth it though.
Avoidance: Since Parry and Dodge both have an requal rate of Diminishing returns, you should try to keep the rating as balanced as possible. If you want to be exact: get around 300 more dodge than parry rating, since that's roughly the amount of parry rating you get through various buffs in a raid.
Mastery: There's no Diminishing Returns and no realistically reachable cap on Mastery, so if you want Mastery, go all out for it.
While gemming you should also keep an eye out for lucrative socketbonuses. Getting a 30 stamina bonus while only losing 10 parry rating by choosing a hybrid gem, may very well be worth it.