I like #1, its a good idea, if doable.
The problem with #2, letting people input stuff on the wiki, is that you'd have people (there's always one) willing to fudge entries to make something they want to sell seem more expense, or the opposite if they're WTB. Of course, if people could input, I'm sure someone could then edit, but then you'd run into dirty edits. Not saying the current system can't fall for this, but this would make it easier.
The problem with #3 would be implementation. How would the parser know if someone's getting a "friend deal"? Or someone is including more money for a previous trade? Or the people are trading multiple items for plat? Its a good idea (I don't mind anonymous data being used this way), it'd just be a matter of if they want to do this.
I think #4, the best choice, is if more people upload their logs to the wiki.
Here's the link.