As of 2014, a $10 bill from 1950 is worth $10. Money is always worth face value unless or until something determines that it is unique and, therefore, more valuable than its face value.
Serial numbers that are odd or unusual sometimes increase the value of money. Some serial number oddities that may make a 1959 $10 bill more valuable include a sequence that begins with a star or consists of the same number repeated. Visual errors, like something printed upside down can also increase the value of money. Regardless of its uniqueness, the condition of the bill also affects its value. If it is ripped, creased or torn, its value decreases.