A broke Mages Guide to Gear

Actually, you are still missing 5 levels worth of damage with level 20 MW, since then a level's worth is 5% more. Haha

Extra HP allows a priest to go MG-less and HB-less at places like DTs and maybe Himes. (I wouldn't know, I haven't gotten my cleric to 3rd, so I don't actually know how much damage they do to a priest.)

Priests need about 1400 HP to be messing around at himes.
Bishops need 2000 HP to run loose at HT after a dispel to take a raw dark wyvern hit.
Seduce Bishops need 4000 HP to be dancing around HT's tail. Any less means death.

In short, yes, it does help in the long run. Really, I think its a matter of patience. You can have this much hp if you either raise meso and invest in hp gear or you wait till you have that amount by means of leveling.