Now that Japan is a member of the Western side, Japanese leaders can't say no to America, and they are buying a lot of American fighter planes. Isn't this a violation of the spirit of Article 9 of the Japanese Constitution, which vows to never wage war again?

Unfortunately, many countries can't say no to America. If you can find it, I'd very much recommend Confessions of an Economic Hitman (link)

When the US strategy became to use Japan as a bulwark against the USSR, they immediately tried to get Japan to overturn Article 9. Luckily the Japanese public support for Article 9 has always been high enough that politicians haven't yet been able to completely get rid of it. So... they just cheat and ignore it sometimes.

As for Snowden, it's hard to say if he's happy in Russia. He was forced to be there. The US canceled his VISA as he was transferring through Russia, so the Russian authorities forced him to stay. Given his situation, he's not going to say anything to upset the Russians too much, so we can't know if him applying for Russian citizenship is just trying to make the best of a bad situation or his real desire.