Brian Azzarello's Dr. Thirteen story arc in Tales of Unexpected (to be released in trade form this week!) has what I think is a great lesson for DC. Azzarello has a lot of fun with the idea of Dr. Thirteen being a professional skeptic, yet living in a world of vampires, ghosts and Nazi gorillas. It's just completely absurd for Thirteen to continue being a skeptic, but that, though, is entirely the problem one has when confronted with the current DC standpoint of "Everything must be shared!"
If everything is to be shared, then certain unique characters just plain ol' cannot reasonably exist in such a framework. A neat idea like Dr. Thirteen does not work when suddenly he exists in the DC Universe, where Thirteen's positions are, as mentioned above, absurd. Being skeptical about ghosts is just plain stupid when you interact with a Deadman or a Spectre.
The same goes for Genius Jones or Lord Andrew Bennett - they do not fit into a shared universe. Homogenizing them takes away from their whole "hook." Take, for example, Tangent. It was a cute enough idea - take just the names of famous characters and have creators come up with brand new characters, using only the character names as a starting point. There were a number of interesting ideas, with one of my favorites being Green Lantern, who could place a magic lantern on people's graves, bringing them back to life long enough to complete business left incomplete with their deaths). Good concepts - and concepts that do not mesh well with having to interact with a WORLD of characters with fantastic powers. It's like making, say, the House of Mystery mesh with DC continuity - it doesn't work well.
It is not like DC does not acknowledge the concept of "distinct lines" of comics. Vertigo Comics are in their own little word, as are Johnny DC comics - but is that really it? If it isn't Vertigo or Johnny DC, then it is part of the "DC Multiverse"? That seems far too limiting of a concept, and it forces things like the Marvel Family revamp, because the Marvel Family has to somehow be integrated into the "DC Multiverse," while doing so strips the Marvel Family of most of its uniqueness, most of its "hook."
Doctor Thirteen makes it clear that he would would work best not tied into continuity - it would be nice if DC followed his lead.