Just checking in here to see whether or not you're aware that Rockbox's rating system is proprietary.
That is to say, if you want ratings, you're going to be doing it by hand on the device for every file you want rated (though once completed, you can export this database configuration across multiple devices which can save you some time and effort if you have multiple players) - it doesn't matter if you have ratings embedded in the metadata of your collection already, we don't use them for some strange reason (I have never bothered to ask if there was a reasoning behind it or if it just simply wasn't implemented), but we could.
Nor does there exist any tool that I am aware of that will export embedded rating info to our proprietary system or vice versa.
Long story short - ratings may not be as convenient to use, or work, as you may expect them to.
That being said, if you already have a favourite theme and are aware of how the ratings system in Rockbox works, you could trivially add a basic rating display in the WPS.
Should you require tuition/guidance in this area, just ask.
Edited to add: A potential workaround I have seen employed before now is to use the metadata comment field (that pretty much never gets used, and if it is used, it is usually used to tell the world what shady site/distributor you downloaded the files from), which we can check for and display, to store the track ratings (having it stored in a standard metadata field also means you could batch edit the ratings from any number of tagging software applications) and display this in the while playing screen. It is functionally identical, and comes with the added benefit of not being tied to the Database (on my devices, not only do I not enable or use the Database, it isn't even accessible - in fact, my main menu screen only has three items in it: Files, Resume Playback, and Settings).
[Saint]