Think of it this way. In one of the Halloween episodes Springfield was terrorized by advertisements come to life because people couldn't stop looking at them. Even one person watching them gave them life. Homer couldn't help himself so they lived on terrorizing the community at large. These over-populated sub-reddits are the advertisements and you're homer.

They're not going to magically turn back into what you onced loved. There's no going back, they are ruined because unlike large sub-reddits like /r/askscience they didn't have a team of moderators diligently working to fight back the cancer every day and now that's all that remains, a lifeless husk of what they once were, replaced by Karmawhores reposting and xposting stupid shit that the Homers will eat up.

If you want a sub-reddit to make a comeback you have only one choice. Spend as much time as you can in the new section of that page downvoting shit and upvoting the good and then convince as many people you can to do the same and you'll have to get the mods on board as well.