Will the gold lock tarnish?

if you're afraid of it... discoloring the leather.. it won't. the hardware will tarnish, like twinkle said, it is polished brass and not gold.

This is 100% incorrect! If your lock tarnishes it can mark up light color surfaces, Such as Vachetta, White Multicolor Canvas, etc. You should try and keep your locks clean as tarnishing is the oxidation of brass - If you have ever wiped your locks with a white cloth, you know how much dirt, grease and other various elements have adhered to the surface over time.
 
Silly question: If you barely use the lock & key, is it recommended to polish the brass every so often (assuming that it still oxidizes regardless of use)?
I keep both in the little box that they came in & store it away from my speedy.

This is 100% incorrect! If your lock tarnishes it can mark up light color surfaces, Such as Vachetta, White Multicolor Canvas, etc. You should try and keep your locks clean as tarnishing is the oxidation of brass - If you have ever wiped your locks with a white cloth, you know how much dirt, grease and other various elements have adhered to the surface over time.
 
These locks are NOT brass. They are just coated metal - so yes - they will tarnish and they will leave marks. LV locks have not been pure brass, or even real brass, in many many years.

Any idea what material they used in 2004? I have a lock that is from my mini HL and it is different than the one from my Idylle Speedy. I actually prefer the newer material because the old one tarnishes quicker (I clean it regularly with toothpaste)... but it also makes my fingers smell like metal (like handling dirty coins kind of smell). I don't have that problem with my newer lock.
 
Yes, this does happen over time but thankfully it hasn't happened yet to my speedy. I put a lock on my bosphore messenger bag's D ring and it tarnished the leather trim around the bag.