Not everyone, but I feel recurring NPCs, good or bad, should be statted to some extent. For example, if the characters go for an afternoon of shopping and resupplying, I don't need stats for all the merchants. However, I might want to know that Ol' Hesterman, who the party often contacts for unusual (magical?) items or rumors has Appraise +10, Gather Information +6 and Haggling +12. Unless he regularly and literally arm-wrestles PCs for discounts, I don't need to know his Strength or probably even his hit points - unless say, he's about to be targeted for assassinations and the PCs are going to have to stop the assassin (or are the assassins).
When the group's rogue goes to pawn a diamond he found without the tax collector knowing, I might have full stats for Finch the Snitch and his two bodyguards, in case the rogue tries to start any trouble (even though the two have been business terms since childhood). And I'd definately want stats for the Lawful Evil priest Axenor the one-eyed, who while dispensing cures to the village in the name of Pelor, has been dispensing vigilante style justice on those who come to his confessional on Sundays. I'll need them once the PCs find out about his dastardly deeds, even if he is their beneficiary long before then.
Stats aren't just for bad guys; they're for anyone the party will come into conflict at one time or another, though usually you only need the stats for what areas of conflict an NPC may present.