The hottest asteroid on the market continued to be the same 2004 MN4 asteroid - also dubbed 99942 Apophis - until the last summer. It was again scheduled to tell us "Hi" on April 13th, but in 2036. Such a Sunday encounter would only take place if Apophis were able to hit a 400-meter-large "gravitational keyhole" in 2029 that would redirect it to attack us in 2036. According to the most recent data, that won't occur.
Some journalists - such as those behind the article you get if you click the picture - can't get the most recent reports. But let us talk about their - currently defunct - speculative collision anyway. The collision would be equivalent to 80,000 Hiroshima bombs which is not necessarily the end of everything - it is only 100 times more than the first H-bomb - but it could be rather unpleasant anyway. The probability of that collision was estimated to be 1:45,000.
According to the most recent data, NASA recommends you to ignore this particular asteroid - it is the first one on the "currently unobserved" list and its Torino scale is already 0 - and it shows 2007 CA19 to be the only one with Torino scale above 0, namely 1 (it has about 1.5 parts per million of probability and the speed during the March 14th, 2012 impact is rather high):
Oh, sorry. The correct URL is here. ;-) Would it be a good investment to pay the estimated 300 million dollars for a mission that would almost guarantee that the asteroid becomes harmless, assuming that the probability were 1:45,000? Note that 300 million dollars is about 8 hours of the Kyoto protocol. I think that the answer is Yes, it is a good but not remarkably good investment. If you estimate the costs of the damaging collision to be the annual global GDP, around 50 trillion USD, the probability 1:45,000 makes the statistical expectation value of the damages to be 1 billion USD. That's why an investment of 300 million USD is still expected to be profitable in average although the margin is not breathtaking. ;-)
It is clear that if the damages would only be as large as 7 Katrinas, i.e. below 1 trillion USD, as some sources say, the calculation shows that the risk simply can't justify the investment.
Correct me if you think that the numbers I use are unrealistic. But I do think that the calculations whether a mission is a good idea or not should be done calmly in the way I sketched, without any additional bias. It may be useful and fun to learn the technology how to manipulate with asteroids but the value of this know-how is not infinite either. The proposed technology is "gravitational tractor" - the spaceship flies next to the asteroid and the gravity exerted by the spaceship on the asteroid is apparently enough, cumulatively, to deflect the asteroid.
You can see that the collisions that are not ultimately devastating and that only have 1:1 million or smaller probabilities shouldn't be paid for.