Building a real Millenium Falcon is pretty damn awesome, no argument there, but if they really wanted to do some good, they should use their talents to build a round sphere like spacestation. About the size of...oh let's say, the size of a moon. Now that would be out of this world! And if they did build this spacestation, we could use this moon sized spacestation for defense, in case their is somekind of invasion from outerspace that threatens our planet. Hell, they could build some sort of mega laser defense system into it, that shoots out a super laser beam at whatever is attacking us.
Now it would also need a propulsion system, at least something to keep it away from the earth's gravitational pull. And it would need to house a lot of small space ships and troops for extra security; don't won't any rebel terrorists taking the thing over, right? And let's not forget, we would probably need some old guy with years of supervisory experience and diplomacy to run the whole thing, who just happens to have a skin problem and can't be in direct sun light, in which case, being in a dark room with minimal lighting and controls at his finger tips, would benefit him and thus he could live out the remainder of his life running the spacestation.
Anyway, that's all I can think of, unless anybody else wants to add to it.
Oh! Oh yeah, a tractor beam could be useful too! I'm not quite sure what we would use it for, but it couldn't hurt to have that as well.