It's similar to our "up", in some cases (i.e., when something "comes up", to "call up", etc) , in the sense that "up" is not necessary but adds some context/feeling... unfortunately your examples probably dont have exact counterparts, i think 聽起來 would be "from the sound of it", or "upon hearing it", 想起來 " come to think of it", maybe think of it as "the thought arises", or "the thought comes up" ? this is how I understand it, does this help?