Yes it's still a good idea, you may on some of the widest 4x4s be able to see down the flanks of one of the narrower caravans. However, the extra safety margin bought about by the use of extended mirrors (and lets face it, they are not particularly expensive) makes fitting them well worth the trouble. I once met a fellow caravaner who towed without them, when I asked him why, he just said that all he had to do was to wiggle the steering wheel a little to be able to see what was behind him.
I haven't found that little golden nugget in the CC handbook yet, but I'm still searching.