The Panthers added to the Sydney Roosters' weekend from hell after Saturday night's NRL loss, with the 20-12 win coming over the Tri-colours feeder club.
Brennan is credited with developing the wealth of talent at the foot of the Blue Mountains, and is considered a candidate for the vacant Gold Coast top job.
After winning the under-20s in 2013 with the likes of Bryce Cartwright and Reagan Campbell-Gillard, he has since claimed the 2014 and now 2017 NSW Cup titles.
"Six years ago the club was nowhere near the position it is now, but with Gus (Phil Gould), Ivan (Cleary) and Hook (Anthony Griffin) they've developed a really good culture in the club," Brennan said as he deflected attention from himself.
"You've got to develop your own, you can't afford to buy them."
Brennan denied claims after the match he had organised to meet with Gold Coast officials this week, and wouldn't talk up his chances while Penrith's season continued into next week's national championship match against Queensland Cup premiers Papua New Guinea.
But his young men did it for him at Leichhardt Oval against the Roos, who finished first in the regular season.
Halfback Darren Nicholls was man-of-the-match for Penrith, while sons of former Panthers Steve Waddell and John Cartwright - Corey and Jed - each scored tries in the win.
Penrith trailed 6-0 on the halftime siren, before Nicholls kicked for flying winger Maika Sivo to score on the last play of the half.
Tony Satini gave the Panthers the lead on the left edge five minutes after the break, before the Roos made a mess of an attempted 40-20 from Nicholls at the back to gift Waddell his try and Penrith a spot in next week's interstate challenge.
"It's fantastic for the game PNG are there. But they don't have to win it," Brennan said.
"Three years ago in 2014 I probably didn't give it the respect it deserved. We partied too hard after the NSW Cup grand finale, it was the first year it was in.
"I won't make that mistake this year."
Photo copyright: NSWRL.The Penrith Panthers have defeated the Wyong Roos in the Intrust Super Premiership Grand Final.