I'm planing on backpacking across Europe next year and I hate being the dipshit who only speaks one langue. I already have a small amount of german and spanish so those are the only two I'm interested in. I get the impression that outside of Spain spanish isn't spoken much but I do plan on traveling south america at some point too so spanish is going to be needed eventually.
German is far more useful (in Europe) unless you're traveling around Spain; the Balkans and Eastern Europe in particular will have a lot of German speakers, the low countries have plenty of German speakers, and of course the Germanic countries as well. That said, Spanish or German pale in comparison to English in terms of usefulness, and there's very few instances outside of German countries (Switzerland, Austria, Germany, Luxembourg kind of) where somebody would prefer to speak German to you than English. If you're planning on traveling to South America ever just learn Spanish instead, it's far more useful globally and has way more speakers than German. It's relatively easy to get by with just English anywhere in Europe that's on the tourist circuit.