I used to have a 306 xsi 16v version......and wanted more power, but to be honsest adding a decent exhaust and filter did very little, short of spending crazy money on throttle bodies/better cams/nos/supercharger......i just would'nt bother. ure better of saving the cash and buying a more tunable car (dont rule ouf the TDI's!).
Shame u could'nt get a 1.8t coz once that remap goes on its like a whole new set of wheels!