You don't have to play NZ teams, but French players have a diet of pretty high quality of rugby, with both top 14 and Heineken cup being probably at least as high as (and probably better) what Super is. That includes NZ teams too, none will tell me NZ and Aus are better without regular contact with SA, why I disliked NZR's decision to part ways although I know many on here have called for it for quite sometime, but I always thought it a mistake. I believe one of reasons ABs were bullied in forwards by French last year.
Geez Derps you live up that way don't you? You must see the quality of rugby the teams are getting on a regular basis. It's not just getting the higher standard of rugby that will make teams/players better, it also comes with good coaching etc. There is a reason thoase teams but the best players from down here, and then they not always stars up there, it's because they are playing a higher standard there.
I would say most players that go up there and return are better players for it, both better good style AND playing against different styles of rugby make for better players. Look at the likes of Nic White etc that have come back from NH, they generally are better players.