It gives you more control of the EQ. You get more advanced EQ. Plus you get additional features such as better folder browsing, themes, battery life remaining in %, many small apps like calculator and calendar, clock, etc. It's definitely worth it.
The risk (no matter how small) of bricking it isn't obvious enough?
Anyway, mine have invariably failed at the jack solder joint. It's rather despicable how poor those joints are for such a high-stress area. My first one failed after about two and a half months (and it bricked on me shortly after implementing the "open it up and stuff-it-with-something to hold the jack down" fix, I believe as the result of a malfunctioning USB port), and the second one took about the same amount of time. I re-soldered it, first using no extra solder (which took all of about an hour to break again), and then again with a little additional solder. Since then, no troubles - but that was only yesterday...
Granted, I don't use right-angle plugs. I have a stock-corded Alessandro MS-1i, and a short patch cord to a portable amp - both of which are straight and probably get more than their fair share of knocks. I'd like to convert both to right-angle plugs (actually, replace both cables with more convenient ones), but that's kind of on the back burner for now.
If you don't touch the EQ, the sound should remain the same. Battery life does get better.....how much better depends on what type of files you plan on using on the player. HIgh bitrate MP3, what I use, the battery went from under 10 hours to approx. 15...FLAC and Ogg Vorbis both start off worse than MP3 in the original firmware, but do better than MP3 if you Rockbox.
Startup is much faster, as is shut-down. All-around it is faster to use.
However, the improvement I like the most (along with the increased battery life) is the ability to sort by album artist. That means that compilations aren't split up into different artists for each song. Folder navigation fixes that too, but isn't as nice to use and certainly is more of a pain with onboard/external memory (and many of my album folders were renamed by the Clip+ because they were too long, apparently).
1) Better bookmarking feature. You can manage a list of bookmarks especially if you are listening to more than one audiobook or podcast at a time.
2) Faster startup. No need to wait two minutes refresh your library each time you take out your micro SDHC card.
3) Better user interface. You can see items that matter to you such as accurate battery indicator (in percentages), bitrate of file, time of day, album name, etc.
4) Better file navigation. If you like navigating by folders this is much easier to do with Rockbox.
For me, using rockbox on Fuze/Clip is complicate what is simple. Besides, I prefer the sound signature/SQ of the original firmware. In flat, Rockbox is inferior in terms of SQ, compared to the original firmware.
And I do not have much patience to deal with the zillions of options in Rockbox... )