If you still want to know what the Nectar does, it basically does 3 things:
1: Makes enemies visable throught objects. Its kind of like the detect life spell in Oblivion
2. Makes your melee attacks much stronger.
3. It increases your accuracy.
Thats what I remember it doing when I played the game, but that was way back in May of 2008 so I may be wrong or have forgetten something.
You also have to remember the iharmful implications it seems to have on the minds of those who use it, espcially frequently or over a long period of time. I think it'd be fair to factor in some sort of reduction to mental characteristics after many uses, or after using it for a long time.
Also, if you wanted to get really accurate in the HAZE universe, when using Nectar any blood and gore should not be visible. Troops using Nectar don't see the horrors of war, thus making them more effective killing machines. Not sure if this is possible or would appeal to many people either, just thought I'd throw it out their. Maybe an optional file, who knows?