I never flashed the bios of a HD. I would do it just cause it sounds cool. I have flashed video cards with new and custom bios, DVD-RWs, a million mother boards... but never a hard drive. Seagate must have gone through the trouble of creating that new bios rom for a reason... It must improve or correct something... I would do it.
Whats the flash procedure? Boot off of a USB drive or CD with dos and run a seagate flash utility? If so it should be quick and easy. If you can flash from windows than thats even better.