Twitter application which only lets people follow that have 30 or more updates?

[Rixyla]

i've have a similar problem, although not on the same scale as yourself. As far as I know there is no such software. However I do believe Twitter seem to be generally aware of this, and suspend accounts that are controlled by bots. I know this because sometimes I get the notification that somebody is following me (unsurprisingly not somebody i've heard of and perhaps related to a keyword that i tweeted) but then go back after a few days into the email to see what that user is and the account has gone because of "suspicious activity"

I think the only practical way is to "protect your updates" in your twitter account settings, but then you are not in the public timeline.
http://twitter.com/account/settings

to be honest i don't really care too much who follows me, i tweet absolute rubbish most of the time