Is there any use for B grade Wanzers other than Quality upgrade materials?

I am a new player. Started playing like a couple of weeks ago. Pulled Rosa judgement and her Wanzer. Having fun using her cutter AOE so far. I have a couple of questions.

1. Are there any B grade (blue rares) wanzers worth keeping or are they just upgrade materials?

2. What should I do with a third set of A grade Wanzer parts? I used the second set to upgrade my first one but what do I do with the third because I can just use B grades to continue upgrading A grade Wanzers.