My personal preference is that displaying agents should leave the received
folding alone if it will fit into whatever windows it is using, just in
case it retains some useful structuring put there by the author.
well, that's sort of why I suggested refolding only the ones that have
encoded-words as a 'conservative' policy - because it's so often necessary
for user agents to add additional line breaks to them anyway.
but I actually think it's reasonable for a receiving MUA to refold
any field.
in my experience careful refolding can dramatically improve the
quality of presentation. so smart UA implementors will probably do it,
perhaps with a "show original format" option for purists.
Keith