I have three improvements I would like to see on the plugins.gradle.org website
It would be really nice to have a voting system for a plugin, that way you can up vote good plugins and down vote broken or bad ones.
Also, it would be nice to more information other than just how to apply the plugin on the individual plugin page. Perhaps you could pull in the readme file from the source control system listed in the config? Or enable a file to be uploaded with the plugin that details more information in markdown?
A comments section for logged in users to post questions about the plugin