As a native Spanish speaker, I think Spanish enables you to learn about a lot of different cultures and points of view. Spain and Latin America are very diverse and language is the most important feature we have in common. For example: Spanish, Mexican, Argentinian and Colombian cultures and people are different, even inside the same countries you find strong regional differences. But if you know Spanish, you're gonna be able to learn about all of them with relative ease. Besides, as you said, it's going to be easier to learn Spanish than Japanese. That is an important advantage.
On the other hand, Japan is an amazing country and its culture is wonderful. If you know Chinese, that probably will help you to learn Kanji easily, you should take into account this fact.
In conclusion, I think you should give them a try, not only one of them. I can help you with Spanish, if you wish.
If you really know your hanzi well, that will give you a huge shortcut to learning Japanese. If you don't really know your hanzi well, learning Japanese could make a muddle of everything. :D
Spanish, on the other hand, is a nice, safe language that should be relatively painless for you to learn whenever is convenient.
You definitely should learn Japanese at some point, but whether that time is now or later is up to you.