Is it worth trying for more?

I think the general rule is too not try for np2, since getting even 1 5* servant is hard. Unless you re a whaler than sure

Scatchach's NP already hits stupidly hard even at NP1 so I'd say stop there. Well crazy luck can happen and if you just started you probably don't have enough quartz saved that spending it all would prove a huge loss(though I may be wrong) so if you like her there's no real harm in going for NP2 unless you have someone else in mind to save for either.