yeah i played the FF3 NES rom earlier this year. really enjoyed it a lot. i think FF2 had a more interesting plot, but FF3 certainly improved the 'Final Fantasy' gameplay immensely and is basically the reason FF4 is as good as it is.

if you want to remove a spell, i believe there is an "item" option in the "magic" menu. use, swap and item? yeah if you choose item it turns the spell back into the item that you originally purchased it as. so you can then use it again on another character, or sell it or drop it.