Yes, luck makes a difference. You might not notice the difference if you kill things very quickly (like my archer, using a luck suit/statue makes maybe a minute difference between drops), but if you're more slow in the killing, like my sampire (don't have any slayer weapons yet), then you'll definitely see a difference.
I can't quantify what the difference is though. I haven't played enough to measure it.
Edit:
And what you kill makes a HUGE difference, but only if you can kill it quickly.
Stick to monsters you can kill in 1-2 shots, use the highest fame monster you can. For example, if you can kill an earth elemental in 1 shot or a revenant lion in 1 shot, you'll get better results from the revenant lion, since it's a higher fame creature. But if it takes you 3 shots to kill a revenant lion, you may get better results from killing earth elementals.
