Okay, Allomantic metals. Let's start with a reference table for those who may be just joining the conversation.
Physical Metals:
Iron: External Pulling metal. Pulls external metals to the Allomancer. Simple enough.
Steel: External Pushing metal. Same as iron, but swapped.
Tin: Internal Pulling metal. Increases bodily input functions, Pulling out more sensitivity.
Pewter: Internal Pushing metal. Increases bodily output functions, Pushing the body further.
(Notes: Tin and Pewter do balance out, as pewter provides a counterpoint to tin's senses, and tin provides a counter to pewter's lack of feeling.)
Mental Metals:
Zinc: External Pulling metal. Pulls on the emotions of others, inflaming passions.
Brass: External Pushing metal. Pushes on the emotions of others, dampening passions.
Copper: Internal Pulling metal. Pulls tight your area in the fabric of creation. This prevents Allomantic pulses and mental Allomancy.
Bronze: Internal Pushing metal. Pushes open the awareness to the fabric of creation. (Or perhaps Pushes out an Allomantic echo pulse.) Lets an Allomancer hear ripples in the fabric.
(Notes: Copper, at least, is indeed an internal metal. Vin can feel a slight buzzing within herself when she burns it, as evidenced in The Final Empire. I believe the same is true for bronze.)
Temporal Metals:
Gold: Internal Pulling metal. Pulls an alternate past into the present.
Electrum: Internal Pushing metal. Pushes out an array of possible futures.
Enhancement Metals:
Chromium: External Pulling metal. Enables an Allomancer to Pull away another Allomancer's metals.
Nicrosil: External Pushing metal. Enables an Allomancer to Push out another Allomancer's metals.
Aluminum: Internal Pulling metal. Pulls away an Allomancer's metals, preventing their use.
Duralumin: Internal Pushing metal. Pushes out an Allomancer's metals, expending them all in one flare.
(Notes:I don't think it's ever been confirmed that the metals themselves are affected, merely their Allomantic effect.)
Shards of Andonalsium:
Lerasium: Bequeaths Allomancy. Alloys create mistings.
Atium: Shows the most probable outcome of a situation. Alloys show different things. (Probably, as witnessed by the gold alloy, malatium.)
The main discrepancy I have with your theories, MellingtonBoots and ShadowKiller, is that Copper and Brass don't affect metals, they affect the Allomancer. This is illustrated in the books, and Brandon even mentioned the fabric of creation in an earlier post in this topic.