Exactly the one rationale I was thinking of, a display of power. I'm sure we keep the stuff that needs to be kept secret out of the view of prying eyes and ears.
I'm ambivalent about Japan re-arming. I see pros and cons.
My dad, who was in the Pacific in WWII would still say a big "NO WAY" to that idea even today. He didn't trust the Japanese to his dying day.
I'm not as ambivalent. The Japanese are a modern, capitalist society, well-removed from the "emperor is god, we must rule the world" mentality of the WWII era. They are also our staunchest ally in the region, and I don't see that changing anytime soon.
Besides, a rearmed Japan would be quite the burr in China's butt, a good thing in my opinion.