Speaking to Mike Hosking on Newstalk ZB this morning, Rennie said he had watched a huge amount of rugby over the weekend and that the NPC remained central to the game in New Zealand.
"It's a great comp. It's part of our rugby fabric here," Rennie said.
"The rugby is tribal. In some of those smaller unions, people may not be massive supporters of Super because their players don't get to represent one team. They've scattered a bit. On the weekend, they get a chance to go down and watch players whose fathers and grandfathers have worn the jersey before."
Rennie knows the competition well. He joined the Wellington Lions as assistant coach in 1999 and took over as head coach the following year, guiding Wellington to their first NPC title since 1986 in his first season in charge. He stayed with the Lions until 2002.
He later coached the Manawatū Turbos from 2005 to 2011, a role that began as a short-term contract, and led them to a runner-up finish in the Championship division of the 2011 ITM Cup.
Rennie said the NPC gave New Zealand rugby something other countries could not match.
"It's a real point of difference from a rugby perspective. It's the greatest provincial competition in the world," he said.
"It's basically semi-pro now, and then it's Super Rugby, which is important to then go on and feed the All Blacks. It's massively important and it needs to be maintained.
"I reckon if you surveyed the country, there's massive support for that competition. It's been brilliant this year. Real credit to all the players and staff involved in it. It's been an excellent product and good for our game."
Fourteen players who featured for the All Blacks in Rugby's Greatest Rivalry are available to their provincial unions for round 10 this week.
Otago and Auckland open the round in Dunedin on Thursday night, with prop Saula Ma'u set to pull on the blue and gold hoops once more.
On Friday night, loose forwards Semisi Ta'eiloa and Simon Parker will line up for Southland and Northland respectively at Invercargill Rugby Park.
On Saturday afternoon, Canterbury will have hooker George Bell and lock Sam Darry available against Manawatū in Palmerston North. Waikato host Tasman that night, and both sides can call on an All Blacks halfback: Cortez Ratima for Waikato and Noah Hotham for Tasman. Tasman will also have Timoci Tavatavanawai in their backline.
On Sunday afternoon, Beauden Barrett will play for Taranaki for the first time since 2020, joined by fellow first five-eighth and fullback Josh Jacomb and hooker Bradley Slater. Wellington head to Stadium Taranaki with prop Siale Lauaki in their ranks.
Bay of Plenty close out the round-robin stage when they host North Harbour at Tauranga Domain, with Emoni Narawa and Fehi Fineanganofo set to feature in their backline.