Well .. IMHO, weight training whether endurance or strength oriented is never a waste of time! Each has their own place in a well rounded fitness regime.
If you're seeking mainly to define but not necessarily build muscle, then I would recommend the Tank Top Arms Rotation. The concept is to work legs, chest & back twice per week, shoulders, biceps and triceps three times per week for maximum definition. Here's the rotation:
Day #1: Pure Strength Chest, Back, Shoulders, Biceps, Triceps
Day #2: CTX Leaner Legs
Day #3: CTX Shoulders, Biceps, Triceps plus cardio
Day #4: Cardio
Day #5: MIS
Day #6: Cardio
Day #7: Cardio or rest
I did this for about 6 weeks, and saw nice results with it.
Happy Workouts!
Nicole