I'm not saying that these posts are bad per se, but I would bet that most HN users like either one type of post or the other and not both. I would also bet that the Techcrunch-types outnumber the LtU-types, so trying to move the discussion towards more technical topics is a losing battle in the long run.
So here's what I'm suggesting:
1. Let submitters add tags to their posts along with their titles.
2. Let people whitelist the tags that show up on their homepage.
3. Using data from 2, it should be possible to cluster tags together, and make ad-hoc subreddits. I'm not entirely confident that subreddits are a good idea, but having the tag co-occurrance matrix would indicate whether it is or not.
Adding tags this way is much less drastic than diving straight in to subreddits, and it has a path to end up at subreddits in the end if that ends up making sense. And if subreddits don't make sense, it should at least make search work better.