Well this certainly is worth watching if you're a fan of Yoko. If you aren't a fan of Yoko or J-pop this is going to be very sub-par. The story (if I can call it that) chronicles Yoko's imaginary life immediately following the events of Gurren Lagann Season 1 (episode 1-27). We get some insight on how under her rough tough (albeit curvy) exterior that Yoko is quite "girly". After about Four minutes and Twenty seconds of Yoko day-dreaming she snaps back to reality (cut the J-pop) and continues on her way. This really is a shameless money grab in exchange for fan-service. That said it is all about Yoko Littner (and her apparent lack of clothing) and for that reason it is not only watchable but worth digging around for, if curvy anime chicks are what you are into (although this IS http://www.anime-planet.com so that would make sense).
TL;DR - As an Anime critic: 1/10
As a Yoko Littner fan: 9/10
As a Music fan: 5/10
As a animation critic: 5.5/10