spreporter - 3 short pages of code = 1.5 million pages generated. If I hadn't been lazy and done 2000 pages of code..... ;)
An observation may be that out of the 1.5 million pages, only about 1000 get 50% of the traffic and the rest get visited perhaps once every couple of months, if at all. This has not appeared to have been a problem for Google BUT around now and at Christmas my sector goes quiet, meaning that there is less content from advertisers and by default more repetition throughout the site. This could be a problem which has arisen recently, causing the drop in traffic/rankings.
I'm also interested in the mobile phone side of things. My site is not very mobile friendly and yet 19% of visitors are on smartphones. They manage to use the site ok but it isn't very user friendly. If Google spots a site which is not mobile friendly, then I understand that searches done on a mobile won't rank the site very high.... is this true? I can see no evidence but I think it is a logical theory.