Of course exchange rates matter. The reason why it was shown in a graph and we are always talking about the future rates is because we decide based on the exchange rates. It's crucial. It helps us to analyze and pick the best date to trade. Hence, if you buy at a lower rate, you get higher amount of BTC which in turn you could you use in obtaining more ripple. Just like how much potatoes you could get in the public market if the price cheaper therefore more french fries you could obtain afterwards. Hope i made it simpler with my examples. But i suggest that you hold on to your btc, it is not yet done in increasing its value. What happened in December is just a normal thing during Christmas season.