Do I need a Today's Plan or TrainingPeaks premium account to access planned workouts?

No, the Planned Workout feature comes with two pre-uploaded tests and seven workouts. To create more workouts, however, an account is needed. A TrainingPeaks Basic account will sync today’s current workout. After the first thirty days, however, a Premium account (of Today's Plan or TrainingPeaks) must be purchased in order to continue using planned workouts via Today’s Plan or a full week of TrainingPeak’s planned workouts.