I understand that the newer rule regarding creating new exchange threads is in place to keep the exchange clutter free, but personally, I think it's silly to have to go back and edit a thread that's a few months old if you want to sell a item a few months later. What brought this up, is that a mod had sent me a warning about "creating double threads" when I had mad a new thread in the exchange. Keep in mind that my last thread in the exchange was created in January and I had forgotten I had even mad it in the first place. I mean to me, if a thread is inactive for over six months, it's dead in my opinion.

I also think it's silly to expect users to have bookmarked every thread they made in the exchange, especially if they had been around for as long as the site's been around. I think that it's reasonable to ask a user to reuse old threads if they are less than a month old or if they are frequent users of the exchange.

You don't have to have bookmarked your thread. Go to your Profile, click on the "Statistics" tab and click on "Threads Started by" yourself. That'll show you every thread you've ever created.

Also, presuming that users have "bookmarked every thread they made in the exchange" isn't a particularly tall order in the first place since they're only supposed to have one, period, but as CK said, your exchange thread can be tracked down very quickly via your profile or the Forum Search (which is how I found your other threads, coincidentally, so I can speak first-hand of its effectiveness.)

There isn't a good reason to have multiple exchange threads, though.
I have one. I use it... well, about every six months. xD I just keep a subscription to it so I can access it easily. Why bother making a new thread when you can just use an old one? I mean, it's not like having to edit the first post and title takes any more time than just making a new thread completely. No need for the extra clutter.

And even if you don't want to do that, you can always just view all the threads you've made and it'll take you right to your thread.

The only reason I could see would be that a 6 month old thread may never get looked at.

I don't know much about the exchange though, are you allowed to bump a thread when it gets to a certain age?

Kalliste, it's okay to bump a thread up if it's six months old. xD

The rule of double posting, or "bumping" a thread generally applies to when the thread itself falls off the first page of the particular forum and you're trying to revive it.

I've seen users reuse threads six months old in the exchange even before the rule was created to only have one thread, and I think it's reasonable to feel that it still has potential to be used. Just because it's not used often doesn't mean it won't be just as effective as a new thread. Update your selling or buying section, and post to let people know that you're selling or buying. People will be attracted to the thread no matter what the age or activity so long as you make sure people see it.