i spent a bit on mine had a lightned and ballanced bottom end, re profiled cam etc for it full exhaust, decat, filter.
at the end of the day DONT touch the engine performance wise you'll get little gains yes you could do all the above plus headwork etc but you'll only get 100bhp at the VERY VERY most.
but what i will say is spend your money on decent brakes and coilovers, get a cat back exhaust to get some noise and make it fun, get your induction kit and put it in the bin, put your airbox back on with a pannel filter, it wont gain you any but will restore the power your induction kits loosing you!