@dunzbumz, what kind of sites replaced our site in serps? Is it brands or shallow blogs?
I saw this behavior with good coding sites, with many code examples, forum posts, explanations ... they have been replaced with shallow blog post, only scratching the topic ( in germany ). In 90% of times useless for the users.
I never could get any good reason why this sites tanked.( also they used adsense to make some money, what imo is more than OK ).