The more I think about this, the more I feel that we are ignoring a crucial section about the development of sentient life. If modern heavily researched science fiction is to be believed, there is more to human consciousness than just the biology of it. After all, chimpanzees and the like have had just as long as we have had to develop sentience, and yet they still fall short of human capabilities. Neuroscience tells us there is not much genetic or even developmental difference between a chimp's brain and a human brain, so there must be more behind it. A commonly suggested solution to this is that human consciousness is truly quantum in nature, and thus is unobservable by modern science. If this turns out to be true, the drake equation could be grossly underestimating how long it takes for sentient life to appear.
This just clicked... I think I know something that could stop expansion of a culture other than extinction.
So with neuroscience, nanotech, cognitive science and the like assuming we don't kill ourselves in the near future we can expect to have 1. Robotic brains more capable than human ones. 2. Cyborg brains. 3. Matrix technology. 4. A full understanding of the universe through simulations.
About the question: Should we be funding XCOM? I'd say yes, but a surprisingly large amount of people don't seem to be that interested in space exploration or anything having to do with space. Like this video MovieBob did a LONG while back: