but wondering how many people may have made too many changes that have a ranking influence
That's a good point, however in our case all of our changes were made in the first 2 months following penguin (may/june 2012) and we have made no seo changes in the last 10 months.
Also, and maybe most importantly, it should be noted that we are in direct competition with google in this niche. Google invested in our main competitor about 2 years ago. I am hopeful for but definitely not expecting any recovery.