even if it's brand new, who needs the parts? that's what you gotta ask yourself. i mean, i'm sure there's probably someone who needs a piston, or a left side case, or whatever, but it'll take you awhile to sell it all.
and, if i needed a new piston, i'd buy a new piston...
if you sell the whole kit, you have a much better chance of selling it right away.
another thing to consider, if it's a used kit, i think it'd be harder to sell. if you got a cheap donor bike off craigslist and built up something for a quick sale, you might be able to squeeze out some extra money. just don't build a rolling death trap...