[This is just my personal opinion]
All decently electrum gaining decks should be completed to 300 games at a minimum, yes. But when a deck is clearly past its time and is no longer an efficient farmer (SGbow, cover & cry, Essence's Duo FG killer, etc), 300 games isn't needed since it is extremely impractal to farm with them in the first place. As long as data is normalized (3 games/FG), I believe that a bad deck should just be put to rest and deemed bad for farming. If a deck consistently performs badly through normalization, there is no point for further testing.