Exhaust Questions.

Im in the market for buying a decent exhaust.What I was wondering is,would I still get some decent gains from only installing some new mufflers.Or should I go for the whole setup.Just really wondering how much more horsepower will buying the whole exhaust bring in instead of just buying mufflers,or vice-versa.

What car?

It does depend on the car. If you just wish to improve flow, often the catalytic converter is the most restrictive point in the exhaust, so changing the muffler won't make any difference.
Even if the muffler is the most restrictive point, your engine may not have any need for additional flow capacity, and a new muffler would not make any difference either.

Its a 96 Ford Thunderbird.4.6 liter V8.Ive only got a couple mods for now,such as a K&N filter,underdrive pulleys.But im looking to heavily modify this car.