My suggestion may look ridiculous but since PG has lost a lot of userbase over the past few years, I think we should at least consider this. Instead of following the approach "Jack of all trades, master of none" I think we should focus on rebuilding those sections of the site that are active, starting with the most active one. Why I say this? Because I have managed about 30 different sites/blogs/forums over the past 5 years (5 of them were my personal ones and other ones were of clients) and whenever we want to improve it, we start by focusing on most active category on the site. Once we reach a certain milestone in them, we move onto another. Now, this doesn't mean that while we are working on the active categories, we neglect the others. No, keep posting stuff in others but not as much as the active ones.
The second part - where we are going to revive the dead categories. Since we are already posting things in them, these threads/posts/articles should be attractive. This is where the marketing team has to do some brainstorming. Come up with some sort of giveaway or contest or anything that asks for a user's full participation in order to win something. For an example, I think buying a $5-$10
Humble Bundle is not a big deal for PG and in that, you get few games that you can use in contests/giveaways.
Wow, this turned out to a lengthy post. In my head, it was just few lines