It doesn't matter how much money you spend here, by staying only here you are committing the species to a single point of failure. Fault tolerant design requires the elimination of single point failure architecture, particularly if the detection and correction of the failing element is difficult or impossible prior to failure.
We are pretty bad at detecting dangerously large rocks flying directly at our faces. Said dangerously large rocks have the potential to kill every one of us in one event. There is no safe mitigation, there is no localized preparation that can eliminate the risk. Parallelism is the only idea that provides the proper redundancy. Extra-solar would be better, but we can't reasonably achieve that yet. We also might not be capable of colonizing Mars yet, but we should all get behind the fact that we really need to.