Zdad,
If your goal in life is to speak to the grocery bagger, then Spanish is more important. If your goal in life is to talk to others in Torah learning throughout the world and to listen to shiurim, then Yiddish is more important.
There are way more shiurim and people talking Yiddish while learning than there are doing so whilst speaking Spanish.
But make sure that when you are picked up para trabajo, you don’t mix up the ropa and basura and take the wrong bolsa.