Uhm, on Ilunabar's case the avatars have personality because she is a writer. In truth they are just her playing dolls.
Don't know how convincing other gods would be at that, but not up to me really.

There is the fact that Ilunabar won't be picking up heroes so the avatars are my way of creating alt stories (though I will start to describe more random stuffo)

Also, Avatar prices go up insanely, 1,2,4,8,16,32,64,128,256,512,1024,2048....
And they don't go down when your avatar goes to dust...