What is a 1979 silver dollar worth?

Likely face value only, just very high grade uncirculated and proof coins have more than face values, none of the coins were struck in silver regardless of mintmarks or date. There is a variety of the 1979-P issue SBA coin referred to as a Wide Rim or Near Date type that does have more than face value.
First of all, there is no such coin as an E PLURIBUS UNUM coin of any type!!!!

E PLURIBUS UNUM is the NATOINAL MOTTO that appears on all most every coin ever made by the U.S. and all modern coins from 1938 to 2012. A one dollar coin dated 1979 is a Susan B. Anthony dollar.They are only slightly bigger than a quarter and none of them were struck in silver. The coin is only face value.