You wouldn't need pickpocket to get any of the uniques. There is a unique armor (Larian's Breast plate) that requires lockpick 5 in order to get a treasure map which then along well some other items will open a secret area that allows you to upgrade that breastplate. You can get two levels in lockpick by joining the Thiefs Guild but in order to join the thiefs guild you need 1 level in pickpocket. So 1 level in pick pocket is good. You don't necessarily have to add 1 pickpocket in your skill tree. Sometimes you can find boots or other items that have that skill. This armor isnt available till rather late because you need 4 treasure maps. The Dragon armor is easier to obtain and potentially is as good.
Joining the thiefs guild is a good idea because Finnigan will give a quest that will give your charactor a 20 point agility bonus. So 1 point in pickpocket is worthwhile if only to get that quest.
