Actually he did partially answer your question, since you did mention that you were possibly considering swapping in a V8. His recommendation was to just trade the car in for a V8, since that would save you a lot of money, time, and headaches.
There really is no reason to look into swapping out your computer. Just get HPTuners and retune it to your desired specs. For exhaust, I would recommend a Carsound Hi-flow Cat, and a Magnaflow Catback. I would also suggest you get a SLP Cold Air intake. This way your car will be able to breath better, along with being eble to exhale better with the new exhaust.