I've been looking at our largest site which consists of three main sections. A custom written hub (classifieds), a forum and a blog. We get new user generated content coming in day after day with some pretty good variety, the site is now 9 years old so it has age on it's side as well. New pages are indexed quickly and "appear" to rank quite well. The thing we are not seeing is any real growth in our traffic despite the increased size of our site, I get the feeling something is keeping this site down but I'm not sure if we need more link juice or if we are simply carrying too much excess (old content) or perhaps Google has us set at some sort of daily limit based on some other set of rules... What I can say is this, more content does not = more traffic which is probably fair enough when you think about it. I just wonder if it's smarter to trim the fat and use our sites content differently in a more targeted way perhaps. The thing we do know about this vertical is that sites we compete against have vastly more search traffic than we do.
Have you though about your 'extra' or 'outdated' content being 'noindexed'... It can still be accessed by visitors and SEs. It's still a resource for visitors. It can still 'pass link juice'. It will no longer 'clutter up' the results.
Maybe, set a type of a 'date' indexing procedure where content over N days old is removed from the index ('noindexed'), or maybe base it on topicality and when N new pages appear on the same topic the older pages are 'noindexed'?
Again, Use at Your Own Risk... If you remove your old pages from the index and they're the ones driving traffic, you will lose that traffic when you remove them and if your newer pages don't rank you just dumped all your traffic.
We can run searches that will return some of the oldest content right at the top of the results so Google is still delivering the deeper pages - to us anyway.. The other possible solution is that our titles are all based on "product" in "city name" so perhaps we are just being pushed out by the local search results. Again when I look at my competition they have sub 50k Alexa rankings and loads of traffic so what we are looking for is the point of difference between them and us. If we can agree that a barrier of some sort exists then what is the key to breaking through?