the cheep HP is in the air box lid mod,power commander and exhaust .
after that it gets expensive. hotter cams will only give you a little top end power over the stock cam.
if i was really going to get serious a would get the cyl head ported, and change the cams. maybe up the compression also.
the 03- 06 Z 1000 already has bigger valves, bigger throttle bodies and hotter cams than the 07-08 Z 1000. also the crankshaft is lighter. all the above mods will hurt low and mid range power. it is a trade off.