nat, you should play the SMS version and describe the similarities / differences between the SMS and PCE versions. That would be awesome .
Great idea, now that I can play the SMS version again via my Dreamcast. I've played fairly far into the SMS port in the past and there are some [very] minor level differences plus the shopkeepers and some bosses are different. The PCE boss sprites are much more detailed and while they are generally different creatures entirely, they retain the same attack patterns. Although I really want to say the bosses in the SMS version take far fewer hits to defeat but I haven't played all the way through so I can't speak for the final bosses.
I suppose I could do some kind of write up a la Black Tiger's nice Magical Chase comparison. Maybe I'll tackle that this weekend (Labor Day!) if I don't end up camping.