Exhaust will help you but it has to be the proper size, if you do your homework on 4cyl engines. It is the biggest no no to go with an exhaust size over 2 - 2.25. People that think putting a 2 and a half on there 1.3 or 1.6 and getting a bigger performance boost out of it, are deffinatly suffering from the placebo effect. 2 and a half piping is to big, the 1.3 and 1.6 need back pressure to run properly so when you put the bigger exhaust on it doggs you out, the only thing its doing it making it sound faster.
For yours, the header and a new intake system would probbly give you some good results, possibly make 5th gear a little bit more enjoyable haha
Amilla