I have a bit of a different take on this. I think the superstars are still out there in the NZ system but we see so much more of them now due to professional rugby & the saturation TV coverage of it.
 
In the "old days" it was a lot easier for players to suddenly burst on to the big stage as there was a lot less rugby & people had barely seen them play due to less TV coverage.  Remember there was no Super rugby & the All Blacks played a lot less test matches than they do now (as they chase the filthy lucre).  So a player would play NPC for his provincial side & rely on newspaper coverage to bring them to national attention.  Therefore players seemed to explode into superstardom when they may have been going about their business under the national radar for a while.
 
These days we can watch every game a player plays in NPC (or whatever cup it is currently called), then Super 14 & even NZ 7's.  He gets heavily analysed by the pundits & the public & any deficiencies are nationally discussed.  We don't rely on some journalist to give his opinion (I remember Frano Botica saying that media support played a large part in him making the All Blacks).
 
Also we tend to view Superstars with a bit of hindsight.  Jonah Lomu set the scene alight playing 7's at Hong Kong but was a flop in his first 2 tests against France in 1994.  He barely made the 1995 World Cup squad due to his struggles at Lozza Mains' tough fitness camps.  I am not questioning his superstar status but this wasn't apparent immediately in 1994.
 
So I think it is a lot tougher for players to be labelled as superstars these days & maybe we just have to admit that as professional rugby & TV coverage emerged in the 1980's & 1990's we were just very fortunate in NZ to have players like Jonah, Christian Cullen & Michael Jones to take that central stage.
 
Saying all that there are some very good young players in NZ that have the ability to make a big name for themselves & hopefully reach that superstar status but the World Cup next year may be a bit early for them (especially as Graham Henry is likely to stick with some of his trusted golden oldies). 
 
  Zac Guildford, Israel Dagg, Aaron Cruden, Sean Maitland, Tawera Kerr-Barlow, Robbie Fruean (if he recovers from what Jacque Fourie did to him at Newlands), Shaun Treeby, Jackson Willison, Luke Braid, Robbie Robinson, Sam Whitelock, Bernie Hall, Bredon O'Connor, Charlie Ngatai.  There's a few names to watch out for!