Dow started his first game since December last year on Friday, having come off the bench twice in recent weeks, and marked the occasion by opening the scoring in a 3-1 win.
"Ryan Dow has been excellent in the last two games so he's there on merit," said McNamara.
"I've said that the whole squad would be important throughout the whole season and bringing in someone like Ryan gives me a problem for next week against Hibernian."
McNamara felt his side fully deserved Friday's win, in which Gavin Gunning scored twice.
"The first half was about as good as it gets," he added. "We were excellent throughout.
"We moved the ball well and had good energy which brought enough chances to put the game to bed.
"It's another hard match against Hibernian next week but let's hope it's another good Friday night result for us.
"If we can play like that then we'll win more games than we lose or draw.
"I thought in the second half it was horrible, a bit stop-start with lots of free-kicks. The penalty gave them a bit of a lift in the second half but we were worthy winners."
Motherwell manager Stuart McCall admitted his players only had themselves to blame for going in 2-0 down before half-time.
"We were very disappointed with the way we lost the first two goals. They were poor and sloppy ones to lose," said McCall.
"But we showed lots of guts ands character to come back into things. I know the character is there to come back from this setback."