Benz gets rid of paper fog - where silver has already started to form in the emulsion before it has started to develop. Benz forms a waterproof polymer when it contacts any metal and this keeps the developer from acting on the grain. Once the the developer starts acting the benz has less effect. The major use of benz is rustproofing. It only works on paper that is fogging because of storage, it won't help with paper that has been fogged by light. It will change the image tone to cold as there will be fewer very small grains of silver in the resulting print as the benz has kept them from the developer action.
I find benz won't completely recover age-fogged paper, but a few seconds in Farmer's Reducer will get the paper back to white before anything happens to the highlights.
Bromide restrains the developer so that a lightly exposed grain takes longer to develop. It will keep the highlights clear but won't do as much for already age fogged paper. It will help with light-fogged paper. It will change the image tone to warm as, with the lessened developer activity, the developed silver grains will be finer.
Finer silver grains are why very dilute developers will form a warm-tone image.