My thinking is that you always want the original. Who knows that if 5 years down the road someone will be able to come up with a new algorithm that can extract a better final result out of the RAWS (look at LR4 vs 2/3)? It would be a shame if it didn't work as well on DNGs, wouldn't it? Also, you can always export to DNGs later.
An a700 and couple of a580s, plus even more lenses.