Ex-England and Spurs star Paul Gascoigne was an unexpected spectator among the home faithful as the Dons' second consecutive penalty miss condemned them to their fifth draw in six league games.
Milton Keynes boss Danny Wilson named the same team that drew 2-2 at Bristol City on Saturday, with Paul Mitchell skippering the side from the holding role of a diamond midfield set-up and Wade Small behind the front two.
Small wasted a golden opportunity to give Milton Keynes a dream start, when his seventh minute penalty was saved by Vale goalkeeper Marc Goodlad.
The 21-year-old's tame spot-kick was gathered comfortably by the Vale stopper low to his left, after Trent McClenahan had been bundled over in the box by Jeff Smith.
Yet Dons were fortunate not to go behind in the 26th minute, when a mix-up between Leon Crooks and Craig Morgan allowed Billy Paynter to run through on goal, but his low strike was tipped round the post by keeper Matt Baker.
Port Vale came out fired up after the interval and on-loan Wolves teenager Chris Cornes' powerful left-foot drive fizzed inches wide before he tested Baker with a fierce right-footer.
At the other end, Morgan, up for a corner, had his effort blocked on line before Vale substitute Chris Birchall got the better of Crooks and fired just wide.
Another lack of communication in the Dons' defence, this time between Baker and Morgan, almost cost them dear a quarter of an hour from the end, but McClenahan's superb last-ditch block stopped Smith's effort flying into an open goal.
And in an end-to-end finish, substitutes Gary Smith and Mirano Carrilho went close for Dons, while the impressive Chris Cornes almost won it with a fierce effort just over the bar for the visitors.