op, headers would probably be one of the least worthwhile starter mods for these cars. as blksvtcobra01 said there are plenty of better bang for the buck mods to do first. the stock exhaust manifolds flow very well even at high hp, and for an improved sound you would do a catback (and then a midpipe if even deeper sound is desired).
like cobrabob said your best bet to start out with basic intake and pulley/tune. the difference from stock is like night and day and you will have a reliable solid car that's capable of running 11-second quarter miles.
of course with improved power you will want to beef up some of the rest for the drivetrain (like clutch and suspension), but basic cpie (chip/pulley/intake/exhaust) is the tried and true way to mod up these cars and has been for 13 years.
like cobrabob said your best bet to start out with basic intake and pulley/tune. the difference from stock is like night and day and you will have a reliable solid car that's capable of running 11-second quarter miles.
of course with improved power you will want to beef up some of the rest for the drivetrain (like clutch and suspension), but basic cpie (chip/pulley/intake/exhaust) is the tried and true way to mod up these cars and has been for 13 years.