just one thing to consider... how do you know we dont have something that they might be interested in having?
there is no way to know what crisis their planet might be going through to warrant stopping in at some "back water" planet like earth. example...
what if their climate is rapidly changing and they are facing a water shortage? 2/3 of our planit is H2O
what other raw materials might we posess that they either never had or are out of.
another point to consider is that no two people, races or species think exacly alike.
Perhaps they might view our use of an airfoil to generate lift as "thinking outside the box" During an episode of stargate SG-1 Thor said it nicely. something like... "Your level of thinking differs from our own... we would have never considered the idea of using sulpher, cordite and a mixture of various explosive powders to hurl a projectile at one's enemy." he was commenting at their weaponry having no effect on the replicators VS our shotguns were highly effective ;-)
another point. - consider all of the life saving medications that come from the rain forrest. Plants which grow on our world would likely NOT be found on their own planet would require them to come to us.
We are just as much a fascinating alien society to them as they would be to us, so i think it is highly likely that we have thousands of things they would want or need that they would have probably never thought of.
When europeans first came to the new world - the culture they found was primative and had little or no technology. Yet look at what was learned from them and what we gained from them - CORN for example was not available anywhere else in the world until europeans came to the americas and spread it to the rest of the world. Same story with cocoa beans.
therefore I believe that it is entirely possible that we have something they may find useful and our planet could offer up many things that would warrant an extra terrestrial visit!
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