even if they did both sound the same, then i would still take the vintage one. since it has a case with it, a reverse wound neck pickup, harder body wood, no gaps inbetween the saddles, and just generally looks better.
although, on the other hand, if it loads of fret wear and other such things, then it'd probably be better to get a new japanese mustang, for playing.
also, the japanese mustang will be much cheaper. so the same goes