Why should you mine?
Well, one reason was because digital currencies are still in their infancy. In fact bitcoin, the first digital currency, was just issued in 2009. Since that time the value of bitcoin is risen. Dramatically as the difficulty of mining new bitcoins increases, the value of the coins have also increased.
Thousands of merchants including dell, overstok.com, newegg.com and many more now accept bitcoin as a direct method of payment for their goods and services as more places accept digital currency. See the value of that currency tends to increase more and more people are mining digital currencies everyday.