Were the 300 listing pages ever receiving traffic? If the answer to this question is no or if a significant number of them weren't ever receiving any traffic it might change what I would think you should do. Poor title tags will hurt your visibility in lots of ways. I would not personally tie the title tag strategy to Panda. Panda is a content algo. It seems to look for duplicate, near duplicate, thin content, poor quality content and then make sure that sites with those criteria are not ranking. If you think more broadly about it you might ask why Google would want to take the whole site down in the rankings for thin content on a few or many pages with potentially low or no traffic. I think the reason they are penalizing the whole site is because they don't want webmasters producing this type of content. If they can get content creators to think twice before creating another 20 urls about x topic then over the long haul their job will become much easier. They can fight off spam more easily because it won't work. I was very angry when Panda 4 rolled out and some sites I own got hit. However, I feel empowered now to correct the issue. My suggestion for you is to compare the urls with their links and traffic. There should be some clear cut low quality stuff that you can noindex. On the pages that drive traffic I would make sure you are providing deep, helpful content. Hard to discuss all the things you may need to do over email but I think you are probably getting the idea. PM me if you want to chat more.
