This is a great topic. In a book I’m writing about online community management, I dedicated a chapter about reviving topics, which sounds complimentary to the article above.
Reviving a category in a community is also a case a-la reviving the whole community – just the scale is smaller.
My experience demonstrated that you can successfully activate a struggling category by reviving topics in it by using different means, like restructuring, retitling to broad or narrow a topic, or change its angle of view, repeatedly inviting members when they are online and many more.
It is absolutely true that a weak community idea makes it much harder to activate members. Still, with the right approach, any idea can find its “followers” and people interested in it. The point here is that you should pay as much attention to smaller things that implement your idea as you would pay to the idea itself.
A proof example would be the following: take 4 Ukrainian communities about keeping goats and making cheese and other milk products (one is mine). There is only one idea those communities are built around. The community mission statements are very similar. However, only one eventually flourished. This means implementation of the idea is as important as the idea itself. As a result, when you think your community as a whole needs reviving, you should also think about reviving individual topics and categories, and pay attention to the current implementation of your idea – before you rush to fix the idea itself.