Buy it done or built

Hi all,

I have a 81kz1000 now. Its a great bike. i am in the middle of a four inch over swingarm project and concerned now about the front end.
I can rebuild the front end to stiffen the ride and perform question is, why is everyone swapping out newer beefy forks from zx7 etc?
1, flex
2, weight
4, some other performance variable I am missing?
I dont intedn to race it on a track but would like to hang with friends on newer bikes. Occasional drag race at the track. All in all a tried and true comfortable "streetfighter" so whats with the front end?

Less flex.
Less un-sprung weight.
Better brakes

Mark