I think it would be pretty much impossible for us humans to work out alien's motivations - thats what alien means, right?

I certainly don't see them needing our resources, we are at the bottom of a gravity well after all. Easier places to get 'stuff' from and there are loads of places and stuff in the galaxy!

I read somewhere (maybe New Scientist, can't find it now) that because of the likely lack of FTL travel with aliens and the subsequent timescales of getting from A to B, they would send a nano swarm first to check us out. So physical laws for soft flesh needn't apply and huge accelerations could be attained, without the need for complicated spaceships, reducing cost and timescales. First Contact is likely to be WAY different from the hollywood view.

I also read somewhere an interesting thought that if you want to meet an alien the most likely place is during a solar eclipse. The thought was that the chances of a moon being exactly the right distance and size to provide a total solar eclipse where you can still see the sun's corona is so slight, that it would be a likely sightseeing destination for aliens galaxy wide. I really like the idea of space tourists. Maybe instead of fearing destruction we should look on it as a tourism opportunity.