It looks like the order that addresses are posted in is kinda weird. It looks like the most recent addresses are posted at the top, then addresses are generally grouped together by month (with the months in a weird order), and the months are generally grouped by year, however sometimes there are one or two addresses that are in a seemingly wrong place.
I originally thought this might have something to do with edited posts, but I am not quite sure about this. Maybe it has something to do with when last an address was posted (even though the addresses are displayed as when an address was first posted)?
They are shown in order of most recent last post with the address. That is because the posts are read in order from most recent to oldest through the show posts page. However the date and link point to the oldest post containing the address.
It might be a good idea to designate some sections as "spam sections" (eg the ponzi section, games/rounds, off topic, possibly some of the local sections) and reduce the value of accounts when a certain percentage of posts are made in these types of sections.
I can make it such that posts in those sections are counted as bad quality posts which will affect the prices with the (now hidden) post quality multiplier.
I am tempted to suggest that you do the converse, and designate sections as "high quality" (eg development, technical support), and increase the value of accounts if they make a certain percentage of "very large" posts in these sections, however I don't want to give incentives to people to post useless crap in these sections, as they are generally free from spam now.
I think that is a bad idea for the same reasons that you said.