Plans for Basic Cost Effective Mods???

I Just bought an AU2 Wagon last week after trading in my old 3.5 litre Magna Wagon. I intend to do a few cost effective mods to attemt to increase both power and economy. For me this involves a few mods to intake of air and exhaust.
On my last vehicle I achieved at least a second off times just with just a few minor changes to the Magna. I used and ITG foam air filter (which according to a dynoe test compair I saw flow better than a K&N for another $10 $20 dollars).
I then heard that they had a very restrictive rear muffler so I changed it for a large redback straight through muffler and immediately after fitment my economy increased from a close consistant 470 km a tank to a close consistant 550km to and from work. I was very pleased with the minimal outlay involved. The Magna was still quiet at cruise. Also got a very noticable increase in power as well..
I put this to test before I traded it it. I did 5 runs from 0 to 100 kph and got readings between 8.5 and 9.0. more were 8.5 than 9s. Stock standard the Magna Wagon is said to do almost identical times to the AU2 Falcon Wagon at around 9.7 0-100 kph as it is almost identical weight AU11 W 1585kg Magna W 99 3.5 1560kg?
Nice to be on the Forum, cheers.