It's even worse for poor Nagato because she's an old figure and the plastic is getting sticky.
But to keep them dust free is basically what everyone else said. Except, I don't have the money to buy a glass cabinet nor do I have the time to indivdually clean over 100 figures and it pains me everytime I see them.
The only ones I keep clean are my Nendos because I do have a cabinet for them (but I'm runnig out of space).