It's really hard to balance everything properly when you start messing with stats.
It's easy to balance out items and stuff, but to do it properly, for each class, goodluck.
What Matt said makes 100% sense.
Bring a mega heal to any class that doesn't have it = demolish every class that does have it.
There's a reason blizz didn't give warriors a lay on hands, it just doesn't belong to a warrior.
Also,
There might be more PvE on this server due to the farming that's required, but there's plenty of people that do nothing but PvP on here. What you're saying is "Neglect them, just focus on my PvE problem".
I'd say think of a way in which you will leave the PvP untouched, but in which you can make the PvE more do-able.
Like an item/object that only functions in specific areas. Which obviously would be some of the instances.
Bottom line,
I support the idea of buffing PvE.
I do not support the idea of giving a major heal to every class that doesn't have one already.