Now, I hope you won't take it bad Dale B if I do not agree with you on putting the objects on layers can reduce the rendering time... that it may affect the refreshing time of the views OK (giving the possibility of hiding all the objs on a layer) but to me it has no influence on the render time...
I propose a simple experiment to support my point of view :

(make sure the bounding hierarchy is checked in the render options from the beginning of this experiment)

make ten spheres with red glass, put them in the same zone of your pic, then make ten cones (with bottle glass for clarity) put them in the other corner of your scene...
all of the objects being in the same layer as the camera (i.e. don't create a new layer)
full screen render in 1024, final, takes 2min40 on my machine
now make two layers, one for the spheres , one for the cones
render time comes: 2min39 ... 0.01 benefit ? much less than 1% (if it is not a clock approx)
return the stuff to single layer, make a GROUP of the spheres, and another GROUP of the cones .. The render times passes to 1m56 :44s benefit (40% or so)
with one group per layer you won't have more benefit... It's worth what it's worth, you just try...
Sorry for contradicting but 'group' and 'layers' are often confusing maybe because some softs work otherwise... Vue prefers groups !
Paul.