The Cobblers leap-frogged Oldham thanks to goals from Giles Coke and Ryan Gilligan, but Leeds' victory at Millwall ended their remote chances of finishing in the top six.
Gray said: "The higher we finish in the table, the more attractive we become to players who we will be hoping to sign for next season."
The Cobblers were always in the box seat and Oldham manager John Sheridan admitted: "We didn't do anything in 90 minutes. Really, we didn't threaten their goal and didn't turn up."
Oldham goalkeeper Mark Crossley twice kept his side in the hunt within the space of a minute in the first half when he firstly beat away a fierce drive by Adebayo Akinfenwa and from the resultant corner he stretched a palm to push away a header from Poul Hubertz.
Northampton had already threatened with a Hubertz header going over the bar and another header from Akinfenwa being cleared off the line by Neal Eardley.
Then just two minutes before the break, Coke burst clear only to roll his shot wide of Crossley's right-hand post.
Northampton went ahead in the 51st minute when a Danny Jackman corner was played into the path of Coke, whose low drive from the edge of the box was deflected past Crossley for the midfield man's fifth goal of the season.
It was 2-0 12 minutes later when Gilligan was sent racing clear by a path from Andy Holt and, although Crossley saved the first shot, Gilligan stroked home the rebound.
There were ironic cheers from the Oldham fans when they finally managed a shot on target from Matt Wolfenden six minutes from the end, but home goalkeeper Mark Bunn was only seriously tested by another long-range drive from Kelvin Lomax in injury time.