The heads are like loose guns, missiles, wings and whatnot accessories. They're small and consequently get lost. I'm willing to put money on the fact there are more headless bodies than bodiless heads. I get the feeling you would too.

Sure the hunt may be very exciting and it would make a great story if you find that last missing piece but I don't think it's going to happen consistently enough that such a collection would ever be complete.

I think it depends on whether or not you're a "journey is more important than the destination" kind of person.