The veteran scrum-half, Test rugby's most capped player, is unlikely to stick around for next year's showpiece in France and this weekend's Auckland encounter might just be his final skirmish with the Wallabies' arch-rivals.
New Zealand won the inaugural World Cup in 1987 but, despite being favourites for almost every tournament since, have always fallen short.
Gregan was part of the side that ended the All Blacks' most recent challenge in 2003, famously taunting opposite number Byron Kelleher with the words "four more years" when Australia had all-but secured a surprise semi-final victory.
But New Zealand have been in sparkling form recently, winning all of their matches so far in this year's Tri-Nations after winning 11 out of 12 Tests in 2005.
"They're a team that has developed, particularly in the last 12 months," Gregan said.
"I think Tana [Umaga] was a great captain, and a great leader, and a lot of these guys have been a part of that team probably since about the last World Cup and even before that.
"They've been a core group of players for five or six years now and with that comes a great deal of experience in dealing with circumstances such as closing out a Test and dealing with coming back from a 10-12-13-point deficit.
"They've done all those things and that holds you in good stead."
In order to score their first Bledisloe Cup win of 2006 on Saturday, the Wallabies will need to stop New Zealand captain Richie McCaw's dominance on in the openside flanker role.
Australia have been penalised in the tackled ball area in their last two encounters with the All Blacks, with Rocky Elsom sin-binned in the first Test.
Gregan is hoping for more consistency from the referees on Saturday, believing McCaw has escaped the bin despite also infringing.
"Referees don't like putting someone in the sin bin, and that's a reality. That's just the black and white of today's game," Gregan said.
"I think the courage of the referee is that they have got to be true to their word, so if that's the case then everyone is happy because it is consistent. As soon as there is inconsistency, that is the grey area."