Are they all robots because thats how all advanced civilisations end up, and is it more likely that they can see our little corner of the universe has no energy resources of value to them?
I think that it would be foolish to assume that all advanced alien civilisations will eventually become robots. Some might, but there are so many possibilities, on so many different planets, that it would be impossible for them all to turn out that way.
A possible solution to the Fermi Paradox could be what you suggested. Why would they go here, and waste time and energy when other planets are more valuable?
However, the lust to explore should not be discredited. Maybe advanced aliens have visited before, and are advanced enough to know to be discreet about it, at least until we have mastered deep space travel.
UPD: Other suggestions about the solution to the Fermi Paradox can be found online.