Can you use BTC without mining?
Yes, for most people it is an easier option to obtain bitcoins through an exchange (or a private trade perhaps) than through mining.

The current market price of Bitcoin is essentially based on a balance between 2 outcomes:


the anticipated probability of Bitcoin becoming completely worthless in future (eg if the encryption failed, or maybe if multiple countries outlawed it)
the anticipated probability of Bitcoin becoming far more popular (and more highly valued) than it is now


The first outcome would probably lead to a price of around zero, and the second outcome could lead to a very high price.

No matter what you believe, Bitcoin is dependent on many factors beyond the control of an individual.

If you hold on to bitcoins, you're essentially hoping for outcome number two.