Couple possibilities - could you self study the semester of Spanish and still have Spanish 3 on your transcript for the other semester? My son skipped Spanish 4 this year and just did the work on his own - mostly just a few tenses and a bunch of vocab.
If not, I don't think it's essential. The academies like to see language, but they really are looking for mastery, which you're not going to get by taking Spanish 3. I really don't think this will be at all a deal breaker, unless of course you plan to major in Spanish there!
Of the two classes you mentioned, as long as they're both credit and show up on your transcript, I think you could make a case for either. If you do a serious job on the gifted study, it would be something you could talk about in your interviews, and you could probably even pull some leadership into it somehow (ie research and then apply the research). Contemporary issues will just help you more with knowing what's going on in the world, which will again help you in interviews (and possibly even giving you some input on what you want to do in life, which academy, etc.).
As long as you're sticking with the math and science courses (and hopefully LA and SS), you really can't go wrong with any of these if you truly get something out of them (ie if you know that Contemp issues is a total "fluff" class in which all they do is watch videos or something - you know the type of class I mean - then maybe go with a different option).