Unless I get drawn into a conversation like this I tend not to think about demographics, I usually just pick a series up if it looks interesting and not because it was published in a mature magazine for mature people.
Anyway, for the shoujo/shounen comments I think you're taking those age guidelines a little too seriously. There are plenty of series that fit into those demographics that are on another planet to things like Naruto and Kimi ni Todoke. The fact that you've mentioned liking Jojo's Bizarre adventure and Dragon Ball make it a little odd to me that you'd find their demographic undesirable actually.
Actually on the topic of demographics I'll post an unpopular opinion of mine. A majority of the popular seinen series really aren't very good. The likes of Berserk, Gantz, Sanctuary and Hellsing just don't do it for me.