headers & cat backs, torque and money

Will I be wasting money on a cat back without having headers? Will I lose much torque by having one or both?

Most of my driving is around town. I don't run much higher than 3500 rpm during normal driving. I'm also running the A/C quite a bit, it gets a little toasty in TX during summer months....March thru November. So having low-end torque is probably benefitial to me, I don't wanna have to run to redline just to get a little acceleration.

Running to redline just wastes too much gas. After putting on my intake I got 22.75 mpg on that tank, I used to be getting 26 in the city.....it's all cuz of my heavy foot. So I'm trying to get my gas mileage higher.

b