Is it possible to simply copy the data from my current encrypted sd card in my LG Optimus Showtime phone (using Android 4.0) to a new unencrypted larger sd card?
Since the phone won't fit both micro SD cards, you'll need to use a PC as an intermediate. Remove the old card and copy the data to a PC after providing whatever password you used to encrypt it.
Then copy the data from the PC onto the new, larger card.