NASA thinks more along the lines of "What sequence of missions do we need to push exploration forward in a particular direction, or to help a particular discipline?". There was already a mission planned to Europa, so they get to pat themselves on the back and say "toldja so". No current plans exist for a lander (we were explicitly warned to attempt no landing).

Like others have said, the Voyager probes are the closest thing to what you're thinking of, I guess. They're still sending back data very relevant to other operational missions, most notably IBEX, and all for pennies in operation costs. [Edit: this stuff] Big missions almost always only get scrapped because the spacecraft runs out of fuel or it stops working for other reasons. For instance, it's predicted that the Juno mission will completely succumb to radiation damage within two or three years, but hopefully, before then, they'll manage to fly it down into Jupiter like they're about to do Cassini into Saturn. BTW, big props to Lockheed for fucking up the Juno spacecraft and thus the orbit, 'preciate it, guys.

I agree with 'bl00, though, no one really thinks significantly "long term" at the organizational level, save governments, and those don't always do the best of jobs. Apparently the primal urge to provide for your children isn't that strong or common enough or something. Serious thought towards 20+ year strategy certainly doesn't seem to be a business incentive if you're paying lip service to the "10%+ growth annually no matter what" mentality. It's also just plain hard to predict the distant future of an institution or business. I'd like to analyze The Vatican's modus operandi more (preferably without Robert Langdon), they've been very effective at staying influential for the better part of two millennia. Maybe all we need to do is indoctrinate everyone!

Recently, I've spent some time planning the next 30 - 40 years of my life. Things look good. I've also given some thought to what I want my mission(s) to do, but never enough.