It seems like the problem might be that there's such a short amount of time to discover good content that gets submitted. During peak times, a submission can be pushed off the first page of /newest within ~20 minutes. If that's a problem, then one solution might be to change the number of items displayed on the new page from 30 to 120.
I wouldn't be surprised if the first page of /newest gets 5x to 10x more views than the second page. People like scrolling; people click much less frequently. So upping the number of posts shown on the new page to 120 should give better content more time to be discovered.
Another idea is to tweak the new page so that the first page of /newest shows every new submission for exactly two hours. That is, page 1 would consist of submissions that are 1 minute to 2 hours old.
Also, maybe some kind of reminder to check the new page every so often would help, but that's probably a bit heavy-handed.