I agree with this idea. Blade thirst is probably the biggest letdown on the ranger spell list because of its short duration. Compared with (greater) magic weapon and even (greater) magic fang it's an absurdly weak spell. To make things worse, while the NWN versions of those other spells were all strengthened in various ways from their D&D incarnations, blade thirst was actually made weaker from the version in the rulebooks. It would be nice if given the restrictions the duration were at least on par with that of greater magic weapon, which every other spellcasting class gets access to.