The on-loan Colchester forward out-jumped the Vale defence to head home after 25 minutes to give his side a well-earned victory.
Dagenham sat ninth in the table before kick off and, despite a winless run stretching six games, could still harbour hopes of claiming a play-off spot come May
Despite their inferior league position Vale started the brighter with Kevin Gall testing veteran goalkeeper Tony Roberts from long range inside ten minutes.
However, following a series of crosses into the Vale area, Guy found the space to meet Ritchie's 25th minute delivery with a glancing header past Joe Anyon.
The goal seemed to knock the stuffing out of a side that had suffered ten league defeats on home territory.
Just three minutes before the break Louis Dodds almost drew Vale level when his shot from a tight angle struck the bar after Roberts had failed to gather Anthony Griffiths' cross.
Minutes into the second half Gall laid the ball off to Dodds who should have tested Roberts rather than snatch his shot wide 15 yards from goal.
Daggers midfielder Sam Saunders should have killed the game off before the hour mark when Anyon flapped at a Ritchie corner from the right, but he someone blazed over inside the area.
Doug Loft's speculative effort in the 71st minute called Anyon into action as the visitors attempted to close the game out.
In a game starved of quality Gall almost grabbed an unlikely equaliser for Vale after 77 minutes, but his rasping 25 yard shot smacked against the crossbar with Roberts beaten.
That was as good as it got for Vale as Dagenham saw out the remainder of the game in some comfort.