Prepare the Basic Simple Syrup as directed, adding the vanilla seeds and bean before bringing it to a boil. Remove from the heat and let steep for 30 minutes. Strain the syrup into a large measuring cup.
In a large saucepan, bring the cold water to boil. Remove from the heat, add the tea bags and let steep for 5 minutes. Remove the tea bags and let cool to room temperature, then refrigerate until chilled.
In a blender, puree the berries. Strain the puree into a large pitcher. Add the tea, raspberry juice and lemon juice. Stir in 1/2 cup of the vanilla syrup, or more to taste; refrigerate the remaining vanilla syrup for a later use. Serve in tall glasses over ice.
The iced tea can be refrigerated in a covered pitcher for up to 2 days.