The main benefit from this that I can see is that El Salvador will attract bitcoin businesses with a lot of money and other bitcoin whales who might move there

The main benefit from this that I can see is that El Salvador will attract bitcoin businesses with a lot of money and other bitcoin whales who might move there and start businesses, employing locals and injecting money into the El Salvador economy. The average person isn't going to use bitcoin and the average merchant will likely never be paid in it.