I have a Rubber Lipped and Clown Pleco, and I know that they love wooden or very heavy fiber... I found that they love a wedge of potato, they tear it up...Also it sinks, They also like the peal, that's where the vitamins are.
God to know--but I would still provide some wood. The fish that eat would do so for the lignin, and I am not sure potatoes provide enough. Without the lignin to feed their gut bacteria, you may have some serious problems down the line.
You should make some sort of greens apart of their regular diet to keep them in top condition. Remember, algae will only last so long and after the plecos eat it, they another source of food.