In ZA (and perhaps NZ), clonal selection probably muddies the issue given correlation with vine age.
Certainly. Even more of an issue in South Africa, where they've been -- and largely still are -- working with shitty clones, and even when there's interest in replanting, there isn't always the financial ability to do so. You can see the difference at somewhere like Ken Forrester, though.
In New Zealand, and specifically referencing white varieties, I don't know that they'd be swapping out their riesling, gewrztraminer, and pinot gris (even though, re: the latter, I wish they'd plant something else) for different clones; they seemed to have lucked into some good ones. But the oldest riesling in the country is only what, 30+ years old, and that the property of a mediocre semi-industrial producer in Nelson. I spoke with Neil McCallum at Dry River about the Alsatian/Germanic varieties for a little while, and he seemed happy with what they had.
I don't know where NZ is wrt chardonnay clones, and I know there are some vines in the north that are pretty old (for NZ), but I'd suspect they're more or less in the same situation as they are with pinot noir, which of course is the major clonal experimentation in NZ. They're slowly getting the Burgundian clones they've been interested in, planting them, and finding that -- for now -- the older vines from the allegedly crappy clones are still making more interesting wines. It'll be a long while, and requiring a lot of Felton Road-style site/rootstock/clone experimentation, before they figure anything out. I do know, however, that could they advance the clock a bunch of decades, a lot of the winemakers with the nice, clean blocks of A/B/C, A/C/B, B/C/A and so forth would like to identify a handful of successes and then plant massale. None of the ones saying so will likely live to see that day, however, unless they jump the gun.
Getting back to whites, I'm pretty sure the Brajkovich properties have been messing with site/clone combos in their chardonnay, but I also seem to remember that the oldest vineyards are still whatever they were able to use at the time, which may or may not have been ideal.
I've not heard anyone talk about sauvignon blanc clones, but neither have I asked.
Frankly, though, almost nothing in NZ except for the occasional vine in the far north is old enough to really address this issue. Talking about differences between 5-year and 20-year riesling is one thing, and not (I suspect) the age range that Pithon was talking about.
