Well, remember that rogues are trained to do this particular kind of attack. Compare to a fighter: The fighter gets more BAB, applicable in all cases, but has to take a penalty to called shots.
The Rogue has a lower BAB that reduces his general combat ability but, in those situations where his opponent is hindered, he can make called shots at no further penalty.
Ahh, that would be a mistake. It is not that touch attacks require less aiming, it is that physical armors provide no protection against the attack.
In the case of the ray of frost it needs to be aimed as well as an arrow but while an arrow may be deflected by the physical armor of the target, the ray of frost is not so much a frosty snowball as it is a sudden decrease in temperature. So the armor itself freezes as does the flesh beneath it. The location of that attack can be the difference between a few points of frost bite damage or causing an ice-crystal aneurism.
All the touch attacks that deal damage that I can think of are some form of energy attack, whether elemental or negative. The touch attacks that do not deal damage cannot inflict sneak attack damage.