Coryfan, I took a look at your pics and compared to your tank mine has more plants but less driftwood. I can't add much driftwood because the bottom of my tank is pretty full. The only DW I can fit in there is one that would be slim, tall, and lean against a wall so it would be no help.
But my tank does have quite a few hiding places now that I'm looking at it. They have behind the small piece of DW, under the heaters, behind the rock, in the cave... Should I just add a clay pot?
Update on the food. I gave algae wafers one more try. I'm not 100% sure, but I think one of the cories figured out that it's food. I'm going to give it another go today. I dropped four in yesterday so the platies were completely distracted, so the cories were sniffing around one they had to themselves. I'm going to give them some more time to eat today. Hopefully I'll see some improvement.
I'm watching the cories now. 4/5 are nowhere to be seen, but one of them is foraging very diligently for some food. He seems very active today. I think he might be finding some leftovers from yesterday's feeding. Perhaps he's starting to feel more comfortable, and maybe the other's will soon too. He's also digging his nose very deep into the substrate. Is that okay?