the only real difference between a full line to just a muffler is potentialy a larger inside diameter. this normaly done to let the increased volume of exhaust gases out. you wont have any major increase in volume so a full line wont benifit you realy. a stainless steel line is always an asset to any car even if it doesnt increase the performance. if your looking for a noise just install a back box but if your looking for performance go for the full line.
now a coulpe of things to take into consideration when your choosing your new exhaust...
1) figure out if your going to turbo the car, if so get a pipe half inch larger than standard ie strd 2.5in go for a 3in line,
2) if your NOT going down the charged path leave the diameter well alone. if its too big itl mess up mgp, its all to do with scavaging (different thread).
3) if the car requires a cat put one in, there plenty of sports cats out there, well worth it.
4) never put a smaller diameter muffler on. itl restrict the flow of the exhausts and put all sorts of stresses on things that arent ment to be under any more stress than they are already.
5) if your not doing big miles, under 8k a year, go for the cheap exhaustman in town, more than 8k a year go for the stainless line. pays dividends believe me.
good luck with your exhaust choices.