Came across an end-of-series note for Figure 17 at Karmaburn:

Final thoughts after finishing Figure 17: The MONSTERS FROM SPACE! element and the Figure itself were entirely unnecessary. The show would have been just fine if Hikaru really was Tsubasa’s twin sister, sent away to live with relatives at a young age. It might even have been better that way.

Figure 17 had enough story in the "Tokyo girl moves to Hokkaido" aspect and with the contrast between Hikaru and Tsubasa’s characters. I didn’t need unremarkable fight scenes sprinkled throughout to keep my attention. In fact, the fights were the least interesting part of the series.

As it happens, I disagree strongly. It is true that there could be a story made out of just the twins, but it would be a different story, not the one told in Figure 17. As I mentioned before, one of the main elements of the story is how Tsubasa deals with the mortal danger. We also see the relationships (with a tragic element for a bonus), and the farm and nature. All elements work together. The viewer is free to focus on any one. Indeed, from reading Lawson one might think it's all about the nature. The rest, however, is still there and cannot be denied.