Launched the website in question in early 2010. 0 backlicks, focus mainly on long tail keywords in a highly competitive consumer goods product.
Originally, here is trend of how traffic seemed to go. New page launched, probably 4 months until seeing good traffic volume. Holds steady at good traffic for 6-9 months and then falls to almost nothing permanently even though I add content to these pages to try and "bring them back to life". Occasionally, but very rarely, can I ever bring a page (even one that saw high traffic at one point), back to any kind of decent traffic.
And every now and then I seem to have a page that will hold strong rankings for a year.
Any insights back of the scenario I described. I'm guessing I'm getting hit with thin content penalties, but is it typical to achieve good rankings for 6-9 months before getting hit with then content penalties?
Could very well be. What's interesting/surprising to me though is that they allow pages to rank well for a while and then penalize the page(s). You'd think I would never obtain rankings in the first place right? And some pages don't get "penalized" for say a year. I guess the inconsistency is mostly a result of so many factors in the Google algorithm.
...focus mainly on long tail keywords in a highly competitive consumer goods product.
This part of your strategy also needs examination, particularly in the context of a competitive market with zero backlinks.
Note that targeting longtail like this is essentially what the content farms that inspired the Mayday update were doing... and that Google has continued to go after sites that specifically target rare longtail phrases.
I suspect you'll have less and less success with this over time. Chances are your pages got a freshness boost for a while... and that they were longtail enough that they may have flown under the radar... but I too was surprised that the pages ranked at all.