There are many reasons. I find the language adorable, the culture fascinating, the fashion innovative; but I also think Harajuku would be the PERFECT place to people-watch. There are so many interesting characters that would be so inspiring for art, and I'd just love to glimpse the day-to-day life of those who call Harajuku home.
Also, just another thing I love; the fact that manga artists are treated like rockstars in Japan. I just think it's lovely that they get so much respect whereas here, it's generally only comic-book connoisseurs that actually know the artists of graphic novels. Like, someone who in this country (or at least in Devon) who wasn't obsessed with comics probably wouldn't know the authors or artists of any. Whereas in a place like Tokyo, I'm guessing it's nearly impossible to be ignorant of a mangaka, because manga is such a significant thing in Japan.