speaking for myself, I'm really glad I played Zero and Ao, but the extremely rough translation for Zero in particular hindered my enjoyment of the game enough that I'm looking forward to replaying it once the geofront edit is done. If you can wait on geofront and don't mind not playing CS3 at launch, I'd honestly recommend it over playing them now. Just keep in mind that Ao will still be a mess when you do decide to play it, but the current Ao translation is a improvement from Zero's despite still being very rough.
barring a disaster, I think we'll be getting CS4 next year, so anyone who decides to wait on Zero, will probably still be able to play it, Ao, and CS3 before CS4 launches.