i don't really think A or B width has much bearing on value.
there are quite a lot of A width mustangs, but not as many as B width. and it doesn't necessarily affect price, thaddeus. i myself would not care either way whether a mustang was short scale with A width, or long scale with either A or B width. i see A width (and especially combined with short scale) as being a novelty. and not in a bad way, either.
but with jaguars, A width is something that isn't seen as often. some people might look at the rarety of A width on jaguars and see it as something they want. but on the other hand, some people may be put off by the prospect of a smaller width. or the value could remain unaffected, either way, by you simply selling the jaguar without mentioning the width (nobody could possibly turn round and complain about it once they had bought it)