restore works this way: if you have 10% u get a 10% chance when killing a mob to get 10% of ur max hp back.
Therefor 8avg on higher lvls is more important.
You can stack restore elsewhere, like bracelet and scn. Resistance doesnt really fall off if u stack, but resotre becomes obsolete if u reach 20-30% ur fine. (EE+8 with restore gives 18 restore with sockets).
Hp restore only works as long as you kill monsters, so pvp and bosses its not so usefull. But 30% is already nice to have since smallest mobnumber is 3, that means if you kill 1 group you get rly close to 100% chance of restoring 30% of you max hp. That sound enough huh?
I mean if you loose more than 1/3 of you life vs 3 monsters, u need something else than restore
Average Resistance for instance