I have purchased everything for WFRP2 and find Renegade Crowns to be the least useful book, even the initial adventures series, the Paths of the Damned, had some useful information here and there. The Companion has a few handy game concepts but nothing major.
The fiction is fairly dreadful, I stick to Jack Yeovil, Brian Craig and Gordon Rennie and some of the collections of short stories. If you can find The Vampire Genevieve omnibus you will be reading some of the best Warhammer fiction ever.
A couple of notes, RoS isn't sold out, The Bestiary is, unless you want to pay through the nose for it or pick it up at a convention. There is no Realms of Chaos for WFRP2, but there is a Tome of Corruption, which has been followed by the recent Tome of Salvation.