the think the content of the solo depends on who your audience is. if it is a bunch of kids at a rock concert, they are not looking for technical excellence, they are looking to be impressed. you can make the solo as musical as you like, but if it looks and sounds like you are playing something difficult, even though it may be technically easy, it will have the same effect.
on the other hand, in more musically educated circles, if you played as fast as you could and hit every drum in sight, you would probably be shot in the face. to impress the people who know, a drum solo has to be like a piece of music, not just a virtuosic performance. for A level music i had to perform alot of solos, which annoyed me as im not great at them, but by far the best one i did was an improvisation around a picture. to class it to be an improvisation you have to have some form of stimulus to work from and develop it into a piece which explored all the musical ideas you could work with from that stimulus without totally branching off and doing something different. i couldn't think of a decent stimulus that gave me alot of freedom, but i found a picture of a painting of a guy sitting outside a posh hotel dressed in rags and smoking a cigar, and i just imagined this really sleazy jazz solo i could put to it.