The removal of {src,}pkgcache.bin is already implemented in /etc/grml/fai/grml/
grml_cleanup_chroot and package gettext-base isn't explicitly installed anymore 
- closing this bugreport therefore.

Thanks again to Carsten: gettext-base (and dialog) could be removed as well

Thanks to Carsten Hey:

/var/cache/apt/pkgcache.bin und srcpkgcache.bin kannst du loeschen bzw per 
apt.conf sagen die sollen nicht angelegt werden und schon hast du platz fuer 
chrrootdings :)

apt.conf:

Dir "/" { Cache "var/cache/apt/" { Archives "archives/"; srcpkgcache ""; 
pkgcache ""; }; }