I have owned both a Clip and a Clip +. My Clip + recently died. I use them mostly for audio books and FM radio. here are a few things I noticed.
The Clip has better FM reception and better station lockon.
The Clip can rewind into the end of previous chapter. The + cannot.
The Clip only jumps to the beginning of the next chapter if you are in pause. The + jumps if you push the forward twice.
The Clip’s “Play previous” would take you back to the audio book from FM, The +'s takes you to last song.
Both have clips that that break.
So I would make the ZIp with better FM reception, able to rewind into the end of a previous chapter, only jump into the next chapter while in pause, and change the play previous function. I think it already has a stronger clip.
2, 3 and 4 are software, I know it is possible. For 1 it should be possible, but I don’t know what has changed.
As others have stated, I like having time of track info, I don’t care about album art, I do care about battery life.
