Get the feeling we aint gonna agree on this one, Colin
I email, having read an interview with a well-known agent who said to always do this. It has saved me from wasting my time by submitting 3 chaps to agents in the WAAYB who accept unsolicited submissions but who are currently overwhelmed. And if they say submit anyway, well at least it might give me a name, some sort of reference.
Each to their own, i think we all find out what suits us best by trial and error.
Maybe sending an outrageous e-card would be more effective.
<Added>The last bit was a joke, BTW!