In Fallout 1, high luck makes you more likely to get special encounters. I think it's more complicated in Fallout 2, though, because of "bad" special encounters. According to the "Frequency" column of this chart, high luck actually seems to increase the rate of bad encounters. Am I misreading this? What does determine what special encounters you get?
http://fallout.wikia.com/wiki/Fallout_2_random_encounters#Special_encounters
http://fallout.wikia.com/wiki/Fallout_2_random_encounters#Special_encounters