jim - // It may or may not be a uniquely human trait to be curious about the world, but what *is* clear is that only those species curious enough about the Universe would be capable of exploring it. The two traits go hand in hand. //
Only if you apply the human trait of curiosity to any other species, and as I keep saying, we cannot assume curiosity, or any other trait of humanity in a species that is not human.
// Since there's no intrinsic need for a species to learn how to travel to other planets in order to survive (in the short term), only those capable of foresight and planning would do so. //
Another invalid assumption. You cannot know what any other species apart from our own needs or would learn, anymore than you can assume that they employ foresight and planning to do anything - human attributes which there is no guarantee that they possess.
As humans we make assumptions - that is our nature.
As long as Mankind has been able to look up at the sky he has been curious about what it is, and who or what may be in it - but that is no grounds for assuming that any other species operates on a similar system of curiosity, or an urge to explore.
We make assumptions, we always have - and that is what drives the common perception about alien life, that it must be curious and interested in us.
There is no evidence at all - they may be, but equally they may not.