Rennie has introduced 20 newcomers to the Test arena since succeeding Michael Cheika in 2020 in a concerted effort to build a squad with sufficient experience to challenge for the Webb Ellis Cup again.
It will be a quarter of a century since Australia last raised the trophy - for a second time - by the time the 10th edition of the global showpiece rolls around in 2023.
Final defeats in 2003 and 2015 have been as close as the Wallabies have got to matching their 1991 and 1999 World Cup triumphs and Rennie knows striking the right balance between youth and know-how is key.
Hence why he won't blooding another raft of fresh talent during the Wallabies' 14 or 15 Tests this season, depending on the final program for the northern hemisphere spring tour in November.
"I'd expect us to have a more settled look around the squad because we've got a lot of knowledge and we've got a lot of confidence in the guys we're using," Rennie said on Tuesday.
"But they've got to perform and, if they do that, hopefully they can build on what they've done so far.
"But we're certainly not going to close the door on anyone jumping out of the pack.
"The door's always open. If someone emerges from left field, they'll be rewarded."
Rugby Australia's re-signing on Tuesday of 32-year-old, 114-Test prop James Slipper is evidence that Rennie is well aware that the average age of winning squads is getting older every World Cup cycle.
"But you've got to earn the right to play as well," Rennie said.
"Just because you've been around a long time doesn't guarantee you being part of a World Cup.
"And what we've being doing over the last couple of years is picking some young men who hopefully by the time they go to a World Cup have got 40 Test caps under them - or maybe more.
"So we learnt a lot last year. We had a tough international season and we've got another one (this year) which is awesome."
In a change of tack, Rennie also brought several seasoned overseas-based players back into the Wallabies fold in 2021, including Kurtley Beale on the end-of-year spring tour.
The coach said he'd welcome the 33-year-old's return to Super Rugby amid reports the 95-Test star was keen to come home from France.
"I was really impressed with KB. Obviously (he's) passionate, desperate to be part of the Wallabies again and his contribution was massive," Rennie said.
"He worked really hard on his game, contributed lots in regards to the discussion and our planning and performed really well.
"He looked really sharp against Wales and his real point of difference has often been his speed and footwork and making sure that's at the top.
"That's probably the challenge for him.
"So if he's coming home, that would be great from our perspective because we'll have a lot more influence from a Super Rugby point of view compared to if he was playing in France."
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