Is the event worth investing Saint Quartz?

Well if you don't mind using SQ on anything other than gacha

Personally i only save SQ to roll my most wanted servants. Unless you start buying SQ, or you'll need bit of time to save them. So I would say not really worth it and only use apples if you have any

Not really outside the event all the ce you got from this banner have incredibly niche effect just pull on fp gacha for mooncell or go for gramps banner

I only use quartz on gatcha. So no for me.

Reruns are easy mode. Don't burn sq for ap on a rerun