You'll probably get a lot of different opinions but I run wide open. Images, file attachments and resources are free to guests without login.
If I'm looking for something and run into a login screen before I can access the content, I hit back and keep searching. My other thought was why make someone register just to see an image or grab a file when the majority of them will never come back anyway.
Yeah, I agreed with past feedback that TH shouldn't have but a price on add-ons they have not yet developed or fixed.
I guess it's worth as much as people are willing to pay. $10 for this add-on would be a good ROI for me, if I was looking for it now.
It's a numbers game. Say for every 10000 visitors you get 5 signups, 1 single post member and .5 two post members. Whatever the numbers are, I like to widen my net by allowing guests to see everything with the idea that they'll like what they see and decide to join. A member who joins for the sole purpose of doing 1 thing and then leaving isn't worth anything to me. (I don't do newsletters).
Not that my strategy is the right one, I just open my board up to how I like to search the web for things. I find that when I hit a paywall, full page ad or blocked content requiring a login, I hit back and keep searching no matter how great the site may be underneath the barrier.