drsaenz, it depends on what and how you ride your bike. Personally, I think all sportsbikes now have more than enough power for the street and most people who ride track. Their lacking areas are braking and suspension. Once you get the factory suspension adjusted, I'd go for SS brake lines. You'll get better performance returns from that than you would a PC, vstacks, etc.
Given the mindset I'm at now regarding current levels of performance of sportbikes for street usage. This is my "must have" list of mods:
1) Suspension - revalve/rebuild or replacement of factory suspension is necessary for 99.9% of all riders. Until you can afford to do so, at a minimum adjust the sag/compression/rebound of the stock setup.
2) Brakes - Replace the factory rubber lines with braided SS. Factory pads are okay for general street use, but if you ride hard or do trackdays/racing replace with better compound pads (ie. EBC HH pads) Wave rotors can help depending upon riding style, but most times are not necessary for the average rider.
3) Hand controls - replace stock levers with better units such as CRG or Pazzo shorties. Better, smoother control, less lever rattle while riding and the shorties will help to improve your reaction time some due to not having to negotiate around longer levers. Be certain to adjust your hand controls whether you have stock or aftermarket for best comfort.
4) Foot controls - Most factory foot controls are sufficient to get the job done. But, nearly all aftermarket sets are a significant improvement over factory units. Again, smoother controls, better adjustability (even if fixed brackets are used) will equate to helping you with your riding style and handling. As with the hand controls, be certain to adjust your current setup to what boots you have and the position your feet are in.
That's it. No exhaust, no engine mods, computers, or electrical upgrades are necessary IMO. The only reason for these would be to eliminate the rear fender, replace the fugly factory exhaust can such as what's on most GSXR's or Kwaks now, or to smooth out the appearance. But, again, IMO these are not required. The four I listed above are for safety and better handling/control of the bike.
Beyond that, spend your money on upgraded gear if you don't have it already (actually that's more important than parts for a bike). Once you have appropriate gear, invest in some "you time" out on the track. Or, take the various advanced rider courses from MSF. Anything to help improve your skills is the best investment, or personal modification, you'll ever be able to do. :thumbup