Welcome to the Q&A Forum

hmm that's very interesting, i've had another look at the stats to give more insight. 150,000 visitors hit the forums from search engines every month, of these only 10 landing pages get over 1000 visitors and 168 get over 100. This amounts to 76,000 visits or roughly half. The other half comes from visits to a whopping 16,222 different landing pages. So whilst manually redirecting those 168 may be a manageable task it would mean the loss of half of the visitors the forums pull in. It also doesn't deal with the problem with letting users still browse the old content whilst transferring the link juice to newer areas, since Search Engines would not take kindly to being treated differently to an actual user.

Personally I would make the root domain a catch-all for every term. You don't need separate pages for each phrase you want to rank for. If the entire website is about the same thing, there's no need to create landing pages for different phrases. (Google also frowns upon this) I would limit the usage of the <abbr>tag to once or twice per abbreviation. You also must realize this is onpage SEO, which is great and it does help, but the majority of your ability to rank for your phrases will come from external SEO.</abbr>