Don't even bother worrying about PageRank. I think the PageRank system is spoof nowadays. 2 years ago I had a PR5 site averaging 150-200 uniques per day. Today I have a PR2 site averaging 2000-3000 unique visitors per day, 75% from Google Search.
You should be aiming on search engine position with those links and not PR. Use relevant anchor text and get as many links from unique ips as possible.
I would like to see a screen shot of that. Its just hard to believe that you have 30k back links and are here complaining.
maybe someone has reported to google, saying bad things about your 'seo success' ...and tada...bam bam