The fact that North Korea donated money that they were not required to give says something about them. Whether they are simply trying to repair a tattered relationship or have ulterior motives, I don't know. But, $500,000 is nothing to scoff at, and countries don't just throw that kind of money at each other everyday.
North Korea had ulterior motives for donating money to Japan. It was a public relations gesture. It also doesn't change now North Korea feels about South Korea and the dangers that South Koreans live under every day. North Korea can't really afford to be giving money to other countries with their own people starving.
No, the donation to Japan by North Korea does not give me hope for warmer ties because North Korea has given the outside world such a cold reception since the revolution. The donation probably was designed to warm up Japan to giving North Korea something they wanted, as opposed to a sincere gesture.
With the way North Korea go about their business it will take a lot more than a bit of money changing hands to warm up ties between the nations. Of course it is good that North Korea made the donation. However, until they really change their ways when it comes to nuclear weapons and the treatment of their people it is unlikely Japan will be loving them.