try ring promecha in springvale (i think) and see if they can rebuild the stock rear shock to a higher spec, set up for your weight?
as for mods, i would recommend a timing advancer rotor... rrp is ~$125 ... gives the bike a lot more 'snap' and makes it a whole lot more fun... might only show an extra 1 or 2 peak HP on the dyno, but madkaw can vouch for their usefulness on the track

mick hone suzuki should have them in stock, they are a factory pro distributor... i think brighton K might have them too
grab a K&N or BMC filter while your at it (worth ringing vicwreckers, they usually have a big stack of after market filters for a bout $40) then a jetkit (ivans or factory pro) ... then some tuning... get the air filter and timing advancer on before the tuning, and make sure the tuner knows how to tune for a bike with air filter and advancer mods - there are many morons out there.
if money is tight, i would recommend getting the bits from the US of A, jetkits are about US$100-110 over there while they are AU$240 here

likewise advancer rotors are about US$40-50 compared to AU$125 here
try ebay or some of these stores:
http://www.hardracing.com/
http://www.indysuperbike.com/