The frightening thing for me is the more I think about flare as pre-exposure, the more my view (expressed in the "challenge" to Chuck's reduced exposure with high flare) seems consistent with Barnbaum's take on pre-exposure of the negative (ie that it doesn't really help)
Perhaps a decent way to think about it is consider paper flashing. This effectively increases the "speed" of the paper in the highlights (analogous to what happens in the shadows when exposing the negative under flare conditions), so that it takes less image-forming exposure to get some highlight detail onto the paper. But while it is easier to get that first hint of highlight tone, local contrast in the highlights is compressed, which can end up looking a little muddy. When exposing the negative this is what we have in the shadows. The effective "speed" is increased which means less image-forming exposure is required to get the first hint of density above FB+f, but local contrast in the shadows is reduced.
So I suppose I can summarize my view by saying that an increase in "effective" film speed due to non-image forming light should generally be ignored. This is because for me speed (or exposure index) is little more than a means to an end - ie getting contrast in the shadows as close as I can to the contrast of the rest of the curve. If the extra speed caused by flare/pre-exposure decreases shadow contrast, I'd argue it isn't "effective" speed at all.