CHAT: I need help with the concept "New World Spanish"

I need help convincing an intelligent skeptic that there is a reasonably
identifiable concept of "New World Spanish" as distinct from "Peninsular
Spanish".  His arguments are as follows:

# It does not seem to me that ["New World Spanish"] identifies a single
# variety of Spanish any more precisely than "Spanish" by itself does, even
# within the varieties of Spanish dialects in Spain itself.  Indeed even
# taking some of the salient phonetic features of "New World Spanish", one
# finds them in Andalucia anyway.  Features of both vocabulary and grammar
# differ from country to country in the Americas, and they differ from each
# other as much as they differ from Spain.  So what is being identified? No
# one thing is being identified [...].  I am open to be convinced otherwise.

I think the error is in the phrase "they differ from each other as
much as they differ from Spain."  Can anyone speak to this with arguments,
*especially* if backed up with references?  The arguments need to be
in English, but there references can be in any language whatever.
Either spoken or written varieties or both may be relevant.

OTOH, if I am quite wrong and there is no such meaningful concept,
do let me know at once.  Thanks.

--
John Cowan  jcowan@reutershealth.com  www.ccil.org/~cowan  www.reutershealth.com
"In the sciences, we are now uniquely privileged to sit side by side
with the giants on whose shoulders we stand."
        --Gerald Holton

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