Miyabi E2 or Astra Yao?

I quit during 1.0 and returned recently during 1.4, so all my polychromes went to Miyabi and, luckily, I got her signature and E1. I'm guaranteed and I'm tempted to get E2... But in terms of account value, should I just save for Astra Yao?

I don't have much 4 stars since I only just started playing again, nor do I have an abundance of 5 stars. I only have Miyabi and Harumasa :/ and whenever I do Shiyu Defense I struggle a lot with Harumasa. Is Astra a big upgrade to his teams and is she really worth pulling for in the next patch?