Wayne said Miles was "Double Gold." I don't know whether that was what you called a gold/gold twinborn or if he made it up on the spot. I like Double as the noun. He's a Double Steel. She's a Double Bronze. Compounding can still be the verb though.
Don't forget that steel affects more than just land-speed. Sazed's attacks on the Kandra guards in HoA were sped up, and he was standing in place at the time.
As for other cases of compounding, here's my take:
Pewter- Brute + Thug = Hulk
Tin- Better senses than savants, but you'd be able to use them separately, Feruchemests store sight in different metalminds than hearing and so forth.
Iron- I'd call this guy a Diver. He'd sink into the ground like it was water.
Steel- Dibs.
Zinc- Mate in 32.
Brass- Better wear metal underpants because I'm guessing you'd burn the clothes off your back. Also, if you set a house of fire by accident, you'd probably asphyxiate.
Copper- I could see a Double Copper being able to go back and actually walk though his memories like he was on a holodeck.
(Wait did I just reference Star Trek before mentioning Star Wars? Rust and Ruin! Fetch me caffeine!)
Bronze- I'm thinking of wakefulness as being clarity of thought. You don't think faster, you think better.
Gold- Already explained.
Bendalloy- ...
Cadmium- ...
Alluminum- I'm thinking of Identity like self awareness, It lets you see yourself as you truly are, better than an Auger even. It might also help defend against emotional allomancy.
Duralumin- His Charisma is over 9000!
Chromium- Vegas Baby.
Nicrosil- ...
Some of these might only be useful if you have the full set like TLR and (probably) Marsh. Kind of like how in Allomancy aluminum and Duralumin are only useful to Mistborn.