Funny, I was just thinking this same thing the other day. The site needs to get better at filtering owned items if they want to promote things for me to buy. It would also be helpful to have a more distinctive marker on pages than the dimmed green cart icon. Make it a red checkmark or something.

Similarly, it would be helpful to add an icon showing that an item on a sale or vendor page was already on my wishlist. The site has gotten slower recently, for whatever reason, and I don't remember everything I wishlisted, which is what the wishlist is for, so being able to add something to my cart directly without having to view the product page again would speed things up all round, while reducing strain on the server. Either that, or speed up the site. I don't want to spend more time shopping than necessary.