In discussing Belgian Dark Strong Ales and whether Special B, CaraMunich or other dark caramel/crystal malts are appropriate in the grist, I think it is important to distinguish which type of BDS you prefer. I'm actually surprised that both Rochefort 8 & 10 are in the same BJCP category as Westvleteren 12 & St Bernardus. Tasted side by side, these beers are significantly different and perhaps in a future style guideline they should really be separated into different categories. The Rochefort style of BDS appears to me to have fairly significant flavor contributions from specialty malts like Special B, while Westy and St Bernardus appear to have little to none.
I strongly prefer the Westy/St Bernardus style of BDS and so far my best attempts at replicating this style of BDS have eliminated specialty malts entirely. That said, I don't think my beers would score well in a BJCP competition because judges would likely be looking for the flavor contributions found in Rochefort style BDS recipes. From a drinking perspective, however, I find the BDS recipes with specialty malts to be okay for a few sips but I quickly grow tired of them, while I find the non-specialty malt recipes to be much more drinkable over the entire drinking session.
I think the thing to remember, that turns out to be something that I am still incredibly short sighted about, is the various deltas between the large scale brewing process of some of the Belgians (the Trappists in particular) and the homebrewer. The specialty malts, as I am coming to see through talking with brewers here, offer the brewer at the homebrew scale an oppurtunity to fine tune and limit the deltas between large scale and homebrew process where flavor is concerned.
To your point, there are some characteristic flavors shared by the best of the style (Grande Reserve, ABT12, Rochefort 8, etc.) but definitely some deltas between them as well. It's a little like brothers that look alike but have personalities that are different enough to warrant the comment, "Funny they are in the same family...."