Valuation of existing Systematic Literature reviews before starting a new one
Yes and yes:

"Can I refer these to justify my review with the fact that they do not cover my whole research area?" When publishing any scholarly research, it is important to demonstrate the originality of your work. If you can show that people have done work similar to yours yet not quite on topic or not as comprehensive, then it shows that you are aware of other scholars' work and that you are clear on your unique contribution to the body of related literature.

"or refer some interesting points raised by existing reviews in my review?" Since the other reviews are similar, then certainly you should summarize and quote them on aspects that do have some bearing to your own topic. After all, you probably learned something from reading them that informed your own work; you should present these parts to your readers for their learning as well.