You should stick to the free weights for more than just benching. What about squats, deadlifts, rows, etc.? They should be part of your routine as well. Forget the ab bench, and instead of buying a treadmill, just run outside. I'd instead invest in a squat rack and some heavier dumbells. You got the bench and a barbell with weights, maybe a pullup bar and a dip station would be something investing in as well.