Smith missed a chance to secure Darlington's first point of the season when he blasted an 81st minute penalty high over the crossbar.
Smith placed the ball confidently after substitute Chris Main was tripped by Gareth Owen, but then ballooned his shot into a clutch of visiting fans.
Dean Windass threatened with an early header for the visitors, but Vale bossed most of the first-half and squandered enough chances to kill the game off.
Richards was culpable with two poor misses, including a horrible miss-kick with the goal at his mercy, before he opened the scoring in the 29th minute.
Doug Loft fed Rob Taylor down the left and he slid over a low cross which was perfect for Richards to fire past the unguarded David Knight at the far post.
Vale's dominance continued in the second-half and as Rob Taylor, Louis Dodds and Tommy Fraser all squandered good opportunities before Smith missed from the spot.