Yes and no. It's true you can simply sell if you are bearish and believe the price will go down, or buy if you are bullish and believe it'll go up. But what do you do if the price stays the same? On spaculator, you can still profit even if price stays the same. Also, if you make a really good guess you can potentially win 10x the initial input, which is much more than on the market.
But the real reason behind this app is the graph - a visualization of average daily guesses by the players. We're not sure yet if this graph will have any correlation to the actual population's opinion, but maybe it's worth a shot.