u need 145 of rare drop for 4 copy of SSR weapon... 8 days * 16 times a day 30APquest is 128, and that not counting AP used to finish daily mission. so natural regen is insufficient for even just SSR weapon.

and this also assuming 4 copy in exchange which we haven't confirmed yet.

to answer ur question, since it following granblue framework the best idea is to save all AP pot and only spend on event that matches element u r building. other event, just do with natural regen to get the easy copies and also daily AP pot and etc.