The veteran striker came off the bench to score in the 2-1 loss at Chivas USA on the weekend, making it two goals in three outings, and Rennie says his presence is so vital after returning from World Cup qualifying duties with Scotland.
"It really is [nice to have Miller back]," Rennie told Vancouver radio station TEAM 1410.
"He's done well coming into the game. He's made an impact on it. He's a very important player for us.
"In some ways, it's disappointing we've had two great games at home, then a break, then missing Kenny for those [away] games has knocked us a little bit - but we need to get over that now and move on."
And Miller indicated that he will only continue to improve as he gets more game time under his belt following a fairly solid offseason.
"I feel good - I've said that since preseason," Miller said.
"I felt fit, I've felt strong. Obviously, I was looking forward to the game today to get back and get back into the swing of things."