Making Power Rangers into an anime would be a cultural adaptation of a cultural adaptation. The Power Rangers franchise was based off of the "Super Sentai" franchise, a Japanese series. Giant robots are kind of Japan's thing anyway. But I do see your point. However, in terms of how mature it should be, I personally find the overall silliness of the franchise to be endearing. If you still want some plot meat in your Power Rangers diet, though, look up the SPD series. It had some decent plot, as I recall.