In the meantime, there is some amount of economic activity around Bitcoin. If you are keeping some coins, it doesn't affect the level of economic activity of others, but it does raise the value of those coins that are economically active, this increasing the size of the Bitcoin economy that can be supported when you and the other savers do eventually start spending.
The size of the economy does not increase because the value of bitcoins gets higher, it increases if there is more trade. People who hold on to their bitcoins do not contribute to trade. The value of the bitcoin compared to other things is just a reflection of how much competition there is for the coins that are available for trade, it does not say anything about how large the total economy is.