Is there a way to filter out people who haven't logged on in, say, 2 weeks? When I add a card to my wish list, I usually click on it to see who would have one for trade. When the list pops up, it's full of people who have been inactive on the site for weeks, months, or even up to a year. Am I missing an option like that somewhere?

There's an ongoing development cycle to update the trade interface to include exactly this type of filtering. I think the admins are a bit busy with their lives at the moment and the code has been a bit more difficult than anticipated, but it is definitely on the way.