I can understand that having the topics about useful resources buried under an avalanche of other posts is a problem - but I really don't see why it's such a problem if people are discussing other things on here. I think you're possibly having the wrong debate. It shouldn't be about how to stop people discussing 'off-topic' issues - embrace that and be glad people are coming to the site - but more about how to separate the useful resources from the mundane conversation, to help those trying to find something specific.
As a suggestion - Why not change things around a bit on the homepage? Get rid of the current 'Latest posts' section (It's not all that useful and on my Netbook it takes up almost the entire screen anyhow!) and split it into two separate forums. Have two large buttons at the top of the homepage - the right hand one is a big button labeled 'Resources'. Anyone with resources to share or discuss can post in here. This could also include the job posting section, and most other stuff in the current 'Teaching' category. In the long run, perhaps an FAQ section here could be useful (similar to the ones on DavesESL, but perhaps with information more recent than 2004

) Under the button, maybe list the top 6 most recent topics. Moderate this forum properly - maybe even have posts moderated and approved before they appear on the site. Anything not relevant gets deleted.
The left hand button is labeled 'discussions' and contains everything else - general discussion, subsections on travel, buy and sell, links to other articles etc. Pretty much let this one be 'anything goes' (within reason, obviously) - Basically don't waste your time moderating this forum, except for obvious stuff like racism/direct personal abuse reported to you by other users. If people want to ruin it, that's their loss. Those prepared to trawl through the crap to find relevant posts can and will do so at their leisure. Again, perhaps have the top 6 recent posts displayed underneath the button.
This way, useful resources are easy to find - they'll all be under the well-moderated, heavily policed, spam and troll-free 'Resources' section of the site, accessible with one click of a button from the homepage. And for those looking for a place to debate/discuss/argue/comment/rant/vent or just wanting to share experiences of life in Korea... well, they can do that in the 'Discussions' section without bothering the people using the site for more serious purposes.
In terms of having numerous repetitive threads - yes, this is a problem... on any forum. I wonder if there's any kind of software out there which could automatically scan the title of a thread and suggest similar, related threads before a user posts? Rather like Google's instant search, where it 'second guesses' what you want before you've finished typing the word and hit enter... Alternatively, is it possible to make the 'new post' button redirect to a customised 'search' page which asks the user to search for existing threads on their topic before continuing to a new post screen?
Anyhow, just my 2 cents... I'm certainly one of the ones who's recently discovered Waygook from DavesESL, and I'm impressed by it thus far. Kudos to the mod and design teams for putting it all together.