It sounds like you're experiencing a penalty of some kind, but I don't know exactly what it is called.
>> Backlink diversification
This worries me. How can you control backlinks and therefore diversify? This indicates to me that they are not organic.
>> 95% of backlinks are related; sidebar, footer links
They may well be related, but then I would also assume that that 95% of your backlinks are non-organic and thus discounted and/or viewed as spam. Footer and sidebar links have been discussed extensively on this forum since Penguin.