The lighter firing pin safety spring will smooth out the pull by removing a hesitation as the trigger bar pushes up the firing pin safety, but it won't reduce the pull. Similarly, the heavier trigger spring has an effect on the feel of the pull as the trigger breaks, but I have never been able to measure a difference in pull.
Take a look at this animation, you should be able to see how a heavier trigger spring has the effect:Glock Pistol Animation
If that doesn't make sense to you, please reply again to this post and I'll try to explain it further. I'm off to the range now, will be back this evening.