The Chinese came close enough to Toutatis to get some exciting pictures, and their ability to rendezvous demonstrates their mastery of navigation and guidance, but landing on the rock is a whole different ball of wax.

Their probe passed the asteroid at a relative velocity between the two of almost 11 km/sec. That it very close to Earth's escape velocity. It would have taken as much delta-vee to slow down and rendezvous with the object as it took to launch the probe off the earth's surface. There is probably a place and time in both earth's and Toutatis' orbits where and when a launch could be arranged so that an orbital match could be achieved very economically. But the the mission might take years, and the encounter might actually occur on the other side of the solar system from us.

It isn't that difficult energy-wise to rendezvous with solar system objects, but matching speeds with them is very difficult. And it makes no difference whether you're climbing out of or falling into the Sun's gravity well, it takes as much energy to speed up as it does to slow down.