Bitcoin has value because it has both scarcity and utility. It is a limited and useful resource. It is important to note that something must be BOTH in order to command a market value, NOT either.
More specifically, I see "utility" as network effect, or network value. Bitcoins can only have value if
other people accept and value them. Many people use
Metcalfe's law as a model for Bitcoin's network effect and value.
We can expect both the value to increase and the number of users to increase exponentially so long as the current technology maintains itself and remains both useful and in a limited abundance.
Bitcoin adoption is a free market process. There is no guarantee of exponentially increasing adoption.