Les:
"Why do the performers send me a great big glossy poster with a picture on it and not much more"

Do you discuss this with the performer? I always ask organisers what they want. Some are very specific: "4 A3 posters, 2 A4 posters, two photos and a bio" - others don't seem to care much or (like you) do their own. Some are quite happy to raid the website; we've got some good pics for this purpose.

But the traditional answer to your question is: in the old days you got one good photo and paid a printer to make hundreds of copies of one poster and that's all you could afford.

Now I make customised posters with venue details, date and time printed on them, and A5 flyers are useful to some organisers, especially if they have the common sense to distribute them at club nights before the one that guest is booked for...

"From a festival point of view, I am amazed at the saturation of very expensive fliers that are sent all over the place. Be honest, how many of those finish up in the bin?"

It gets your name known, subliminally and cumulatively. It contributes to making the difference between "who?" and "oh, yes, I've heard of them"...

Anahata