should i try to NP2 Raikou or just save up my Quartz

Your chances of getting a 2nd Raikou is very slim, so I'd suggest saving you SQ for other banners.

The jump from NP1 to NP2 is also not that significant.

Unless you just have an insane amount of quartz, just save up. The benefits of going from NP1 to NP2 are not even close to enough to jeopardize your chances of getting other amazing servants. That being said, if you Raikou is the only servant you care about, then go ahead!

Also, congrats on bringing Big Mama home!