Jeff and all,
An intersting read, if you are so motivated, would be Gary LaFontaine's "The Dry Fly New Angles".
Gary spends ALOT of time discussing attractors vs imitations and why/when each works. I'm not saying he's right but as with most things GLaF, you'd have a hard time proving him wrong. It's a convincing story and a fascinating perspective.
Even goes so far as to design and test the ultimate attractor(my paraphrase), the Double Wing.