In one of my more popular plugin's settings page, I have a box called "Like this plugin?" as the title. Beneath it is a list with three links:

* Give the plugin a good rating.
* Donate a few dollars.
* Get me something from my wish list.

This was sort of an experiment I started a couple of years back to see what would happen with this type of thing. Guess what? This plugin has the most ratings and given me the most donations.

I think you just have to make it really obvious/easy to users. Many users are never going to come back to a plugin's page after initially installing the plugin. Basically, they have no reason to do so. But, if you give them a quick and easy way to do these things, that all changes.

Obviously, this is just from personal experience with a single plugin, but I think it's been an interesting trial-run thus far. I really need to write a blog post on this at some point.