That's about 4.38% annual return over 40 years. Not terrible, but could have done better investing in something else.
EDIT: The brother paid $18,200 for the dime. But my original number of 4.38% was off because I used the inflation adjusted $90k cost. More accurate number is 8.64%.
My numbers are off, but I think you missed the part where they paid $18,200 for it. I had used the inflation-adjusted $90k previously. Using $18,200, the ROI is 8.64% - which isn't too bad.