Another mission to a world we've been to before will yield more interesting science that one to a world we've never been to before? That seems unlikely. Not saying there isn't a heck of a lot more to learn on Titan, but your reasoning here is bizarre.
The fact of the matter is, we don't know what we'll find if we go looking at Europa. One of the things about science is, instead of trying to find the answers to questions like that by just thinking about it (i.e. the philosophical method), the scientific method involves actually looking instead of merely guessing. If we want to know what we'll find on Europa, we'll have to send a probe and actually see.
You could fill a book full of perfectly reasonable statements about what we'd find on planets before we sent probes to them, all as reasonable as what you've saying, based on what we thought we knew at the time, and all dead wrong.
A mission to Europa is far more likely to yield scientifically interesting results than another mission to anywhere we've been before.