OK let me be as evenhanded as I can about this: true, you have plenty of time to take what is "necessary" or "required" later. If you are passionate about taking Japanese, your eagerness will make taking it a breeze. I took Spanish in junior high school, like many other New Yorkers because the only other alternative in New York in my area at that time was French (which I did take later in college). And true, I remembered very little of it, or so I thought. But the rudiments were there and decades later I had the opportunity to have use for it, and surprisingly it came back (living outside the country in a Spanish-speaking country didn't hurt either). More importantly, in whatever hospital I ever worked in, in whatever state, Spanish came in handy quite often, and having me around beat waiting around for the hospital translator to arrive.
As far as beyond medical school, it is a selling point in this country (all other things being equal), and I have been told by several program directors that it would be an asset to have someone in their program who is fluent in Spanish. I also should add, anecdotally, that one of my interviews was conducted in Spanish, wherein I had to interview the interviewer acting as a patient coming to my office with chest pain. He wanted to ascertain the veracity of my being bilingual.
Just some food for thought. Good luck in your decision-making.
