Cockroaches are supposed to be one of the last critters standing after nuclear war because they are supposed less vulnerable to radiation than most other things. An asteroid strike would not produce much radiation. So the rats and other non-specialized critters would also have a chance at world domination. I would include humans in that group, but not all 7 billion or indeed most civilizations.

As for spending more money to insure ourselves against relatively small asteroids. I would wager that what is spent worldwide, on baldness treatments, fake boobs or even football jerseys never to be worn on a football field would more than cover the amount of money needed. Like all politics, it is simply a matter of placing the proper priorities.