Fire ratings are a bit of a sham for somebody that lives in an urban environment. Face it, if you have a fire the likelihood of the FD taking more than 1/2 hour to respond are virtually nil.
Spend your money upgrading seals to prevent water intrusion and increasing anti theft possibilities i.e. reinforce door frames etc.

If your out in the boonies where it would take the FD an hour to respond then upgrading the fire rating is worthwhile.