I think a filter would be extremely helpful, why should I have to waste time even reading product descriptions for items I can't use? Not to mention the page load times. It also would be helpful to have the option to filter out what I already own. The less stuff I have to wade through that I already have or can't use the more time I can spend looking at things I might actually buy. Yeah, I know the icon is a (slightly) different color, but still it would be far faster to not see them at all and only be looking at stuff to buy.