In case you haven't checked out the Rockbox Databox search plugin, you might want to.
http://www.rockbox.org/twiki/bin/vie.../PluginDatabox
It's a powerful search feature that lets you create, on your player and through your player alone (that is, no separate computer is required) a search query to search through your player files via tag parameters (e.g. year, genre, artist), but not just literally (for example, you could create a search to look for music from 1970, or from before 1970, or from after 1970). It creates the search query, and then saves it into your player's root directory. You then play that search, and it, in turn, creates a results file that you then can play, playing the music that meets the search criteria.
The system is a bit cumbersome right now and requires some experimentation, but is a way of doing database searches and playing them without switching to the db; and of doing searches that the db itself does not support. (E.g. by year or genre, as someone was asking about recently, or by ranges.) As noted at the related Rockbox PluginSearchengine page, it would be great if some talented programmer were to pick this up and simplify the process, such as, as suggested there (for example, allowing for creating and running the search as a single step; or even creating and running the search and then playing the result, if that were possible; also, I think that the query creation process could be made clearer).
But in the meantime, definitely something to check out, and it's a good thing.
Thanks, devs.