Light, high-rep workouts are fine occasionally, if you like them, but it doesn't seem like you do. You'll get to your goals more effectively and efficiently if you do more heavy training. Whether that heavy training will make you big or just toned depends more on your diet (and other factors, like how much cardio you do) than on the workouts themselves.
Gunnar Peterson says "If you want to get big, eat big," and folks who want to gain significant muscle increase their calories as well as their weights, and reduce cardio to a bare minimum (to keep it from buring calories that would go to muscle building). Stick to your current calorie intake, up the weights, keep in cardio, and you'll be on your way to getting lean and defined (which just means 'muscle tone + lower body fat').
Circuit workouts are good for burning more calories when working out, and getting somewhat of a cardio effect from weight training, but they don't have to be 'low-weight/high rep' workouts. Several P90X workouts (and P90 Masters "Sculpt 5-6) are built in a circuit fashion, and are moderate-to-heavy weights with low-to-moderate reps (you choose your own rep count and weights).
'lean and defined.' If you find you're getting different results than what you want, then change your program. (IMO, mesomorphs can get better results getting 'lean and defined' using lighter weights and a higher rep count than can ectomorphs, for example).
HTH!