Like some other people have said , unless it is one of those projects were you have a lot of money and would like to see what some 5 grand can do to a standard-sport bike then it may be worth seeing , hell I work on an investment bank and see people lose 200k dollars on a bad investment some times, 5 grand is really not a lot to invest if you are curious .
But like other people have suggested , buying a faster bike from the get go it is the best bet, I ride my bike because the insurance rates , chances of for the bike getting stolen and gas millage are ridicously low, a good mix of economy with some grunt when you need it and head turning awesome looking design.
Upgrading a 650 into a super sport although nice it, would be a travesty of what the bike was originally designed for, however in the case of someone that owns a 650 on a place that has heavy tax penalties on faster bikes or in my case were the insurance rates on sport bikes are ridiculous I would consider it , hell the difference in insurance rates between a new 636 and a 650 for me (because of were I live) is about 2 grand , so if you think about it , if you invest 4 grand on a 650 you would get your money back in insurance savings alone.
Best bet on my case would be to buy an older 636 sadly..
"And the world will be better for this;That one man scorned and covered with scars;Still strove with his last ounce of courage;To reach the unreachable star."