In any case, a nearby planet or its orbit would seem to be the most logical place to start for any supervillain species seeking to colonize its galaxy. :-)
You’re making a big jump to conclusions there. Globally we (EU and US) do care about this risk and in fact are spending hundreds of millions per year.
Or at least we were spending that amount. There’s some idiots cutting that budget in NASA AFAIK.
Let's say being multiplanetary gives you 99% risk mitigation of asteroid decimation.
My point is that we could pursue that level of risk mitigation via detection and deflection methods by pouring more money into it.
It is obviously far cheaper to achieve 99% risk mitigation by dumping money into detection and deflection than it is to colonize another planet to the point of self-sufficiency.
A couple trillion dollars might get us to a basic self-sustaining colony on Mars, but you could defend earth, and all of its immense natural and man-made assets, to a similar degree for orders of magnitude less money. We already choose not to do this because we don't care to achieve that level of risk mitigation even at the lower price point.