COVER 2 baking sheets with wax paper; place 12 wafers, 2 inches apart, on each prepared baking sheet. Set aside.
COMBINE granulated sugar, brown sugar, cream and water in 3-qt. saucepan; cook on medium heat until sugar is dissolved, stirring constantly. Cook, without stirring, until temperature reaches 235°F (soft ball stage). Add margarine. (Do not stir.) Cool 30 min. or until temperature of sugar mixture is reduced to 150°F.
ADD pecans and vanilla; beat with wooden spoon 2 to 3 min. until candy begins to thicken but is still glossy. Immediately spoon 1 tablespoonful of the sugar mixture over each wafer. (If mixture becomes stiff, stir in a few drops of water.) Cool completely until firm; peel from wax paper. Store in airtight container at room temperature.