I think that since the music industry now a days is so demanding for new and unique artists and styles, I reckon there wasn't necessarily a target audience for this song, but instead it was intended to really put herself on people's radar (due to the element of controversy since no one had really touched on that topic before)
A "what if" that I have always wondered about (but obviously won't ever know the answer to) is whether or not Katy would have become popular if her first single had been either "Hot n Cold" or "Thinking of You". Katy had narrowed her choice of first single down to these 3 songs. "Hot n Cold" and "Thinking of You" are both non-controversial, but would they have been unique enough for radio stations to play them by a then completely unknown artist.
For what it's worth, the radio station that I listen to (an adult contemporary station) does not and has never played "I Kissed a Girl", but it did and still does play "Hot n Cold", as well as all of Katy's other singles (but not "Thinking of You", for some reason). Apparently they thought "Hot n Cold" was good enough to play when they had no precedent for playing Katy's songs at the time.
I think that with "Hot n Cold" she would've been just as successful, however I'm not so sure about "Thinking of You". I NEVER heard ToY on the radio, and actually, I hated it when it first came out. I don't think I warmed up to until I heard her sing it live during the California Dreams Tour. I don't really know why, maybe just because I was a little younger and I didn't really listen to songs the same way I did by the time I was 19. Now at 21, I respect her song writing so much, and I think that's how ToY transformed into one of my favorite songs. Hearing it live really brought it home to me, too, and having an experience to relate to.
I think HnC would have still sold her to the public because it IS fun and catchy and a typical pop song. Like I mentioned, I was pretty young when KaG went big, but I did listen to Katy when she was on Myspace, I even had Ur So Gay on my page. I sometimes wonder what if Ur So Gay was released in the capacity that Kissed A Girl was...
I too have never heard Thinking of You on the radio. In fact, I didn't even know it existed until I found this board. I wonder why it is that most radio stations never played it.
If Hot n Cold had been Katy's first single, and if it did make her famous like I Kissed a Girl did, I wonder if it would have caused people to take Katy more seriously, and if Thinking of You would have also been a bigger hit. Again, we will never know. I Kissed a Girl seems to be one of those songs that you either love or hate, whereas basically everybody likes Hot n Cold (except for people who don't like any current pop music, but they're obviously not the target audience anyway), but would an unknown artist have been able to break through with a non-controversial song? Hot n Cold has a 90s throwback dance club arrangement, so it could have been popular with adults who grew up during the 90s, as well as teenagers thinking it was something new, at least to them. Again, I wish Hot n Cold was her first single, but again, I admit I am biased, since I like Hot n Cold but I don't like I Kissed a Girl.
Another thought experiment: as I mentioned, the radio station that I listen to never played I Kissed a Girl (and still does not). During the summer of 2008, they constantly played Sara Bareilles's Love Song. That was the first I had ever heard of her. At the time, I just assumed that was the song of the summer of 2008, and was surprised to find out that it was not a #1 hit. It seemed that adult contemporary radio stations played Love Song as an alternative to I Kissed a Girl. Again, we will never know, but if Katy had released Hot n Cold as her first single, would Sara Bareilles have become as popular as she did? Adult contemporary radio stations would have likely constantly played Hot n Cold that summer, so Love Song might not have become as big as it did, if it would have gotten airplay at all. I like Sara Bareilles a lot, so I am glad that she has become popular, and I do wonder how much Katy indirectly had to do with that.