Currently we are playing with the following variants:
1) wall movement: instead of 3 cards we draw 4 cards. So the wall room becomes a bit more dangerous.
2) replacement character starts in the lava room with half of the treasures (round down) from the first character who died. Now he has a little bit more chance to gain on the others.
3) To enter the river we use the same rule as to exit the river. If you have too many treasures entering the river they could pull you down the water. This makes the river more dangerous and the option with the bridge more interesting because it should be the saver way to the exit.
I know that one of these ideas (the walls) is one of the cards in my Adventurers Variant (see the files section). There are also lots of other ideas to make the temple more treacherous and fast-paced (like a faster boulder, for example). You should take a look.