Well, your decision entirely depends on your outlook towards bitcoin and your risk taking capability. If I see a 30% drop in bitcoin price, I would happily buy more bitcoins to take the benefit of dollar cost averaging method. If I buy at that price, it will average out the buying price to a lower level and the profitability will increase. It will also keep my portfolio risk at a very low level. In one sentence, a large percentage drop will open a new window of opportunity to buy more bitcoins at a lower price point.