I didn't see it in the first post, but the ability to view a different members collection and compare it to your own. For those of us who want to compare sizes. Would also give the option to trade besides buy/sell/trade. I go to a users Trade collection compare to my main collection or if possible more detailed like my wanted section. Would be easy to compare and see what I could try to obtain. If you even went so far as to add a conditions check box so that it only shows what they have that I don't, or what I have that they don't. Yea pretty much sounds like i'm practically asking for the create a trade option like gametz or cag marketplace have. Could even at that point click a create a transaction checkbox, where a transaction can be created that would could be accepted, rejected, or appended.
I'm not so lazy that I'm opposed to the current way, I make do, but it might be something to consider in the future.
Or does the collection tool already allow you to search for an item, and see who has it in what collection?