Seeing as polystone has a pigment, it would fade the colour of it. It wouldn't actually damage the polystone itself. Of course, most polystone items are painted, so sunlight would definitely damage the colouring of the paint.
Just keep your collectibles out of the sun.
When using any aerosol, give it a test burst away from everything. When using compressed air, never hold it close to the items you want to dust. It will freeze the surface, damaging your items.
laudel7, you can get air cans from most hardware shops. For your detolf's, you might want to find some rubber tubing to take up the gaps.
Best thing is, use a brush, if you find you can't get into some area, use a jet of air. Personally, I wouldn't use any chemical product on my collectibles. Some swear by it, so they must be happy with it. I'd rather wait for reports after five years of such use.