Hey, a 03 sporty still as the trap door for the trans, which is a plus!! your scoot is 520 lbs dry and you say the chair and passenger are more than that?!? wow!
A 1250 kit with some head work and some N4 cams would give you an increase of close to 50% more HP and TQ which is nothing to sneeze at! Probably looking at $1900 if you do the work yourself.
The wheels are 19" front and 16" rear with 3/4" bearings, you can fit 110 tire up front at the biggest, the rear is a little diff. tho so them rims might not fit, changing the front tire from a 19 to 16 will change the tracking plane, you might have to do some adjustment with the fork tubes in the triple tree. All things you have to calculate within your total cost!
If you want an idea of how good a 1250kit really is....I have over a 145K on mine with no issues except burning rubber if I'm a little to aggressive on the throttle :)