Nickel, brass, Teflon, zinc rust-busting etc.: which of these have been shown to enhance chain performance either by way of reducing friction or rust? I think I've read comments about certain types creating problems by degrading into something that increases wear but I can't remember the specifics. Are they mere marketing gimmicks?

These coatings are primarily to inhibit rust. They aren't marketing gimmics but aren't essential either if you keep the chain reasonably clean and dry it after getting caught in the rain. Friction reduction is what chain lubes are for.

I still find that I need a very fine film of lube over my chain as a protector. Otherwise I can get lots of rust within hours of riding.

Chain lubrication reduces friction.
My way to reduce friction on chains for the past 40+ years of cycling is the hot wax method.
No oil, no greasy black stuff, no 'magic' ingredients. Plain old canning wax does the trick.

IMO regular cleaning and lubrication are the keys to chain performance and longevity. Nickel plating seems to keep the outsides looking shiny longer but will quickly be eroded from wearing surfaces leaving the underlying steel exposed.

Wippermann sells a stainless steel chain with improved rust resistance but it's not really rust PROOF because the grade of "stainless" required for strength and wear resistance is not corrosion proof. It's also pretty pricey.

The hot wax method mentioned above is an adequate lube in dry, clean environments but useless in rain.

According to Wippermann "The inner link of the 9sX model is made of high-tensile stainless steel that increases the life span of the chain up to 20%" No steel is truly corrosion proof, hence the correct "corrosion resistant" vs the common, but incorrect, "stainless" designation.

These guys claim (take it with a grain of salt of course) that their coating does not come off with use but I do not know of anyone that really put that to the test yet. https://45nrth.com/products/category/chains

Wippermann says the 10s1 and 9s1 chains are all stainless steel, both inner and outer links. The 10sX and 9sX chains have stainless steel inner links and nickel plated outer links. And, yes, they are corrosion resistant, not corrosion proof.

Nickel-chrome looks nice and shiny.

Even Teflon (DuPont's brand name for polytetrafluoroethylene aka PTFE) won't cut chain noise from insufficient lubrication or derailleur mis-alignment although it might be quieter than an untreated chain.

even nickel plate is mostly cosmetic, the outside plates wont look rusty,
but real bearing/bushing surfaces the 1st day of use takes off the plating ,
and then it's just steel .. you need to keep a bit of oil on, and dirt out of..

The new 2013 Dura Ace 11 speed chain is claimed to be a 20% wear improvement over the previous (cs-7901) chain. They say this is due to teflon coating. Have not seen one, but it's in the 2013 trade sales and support manual.

What about the titanium nitride coated chains from Shimano, KMC, etc? What does that coating do, if anything?

https://draco.nac.uci.edu/rbfaq/FAQ/8d.2.html

I don't know if it's still true, but back when I was still in the Bicycle Industry, the pro teams found it more cost effective to use generic, unplated chains and just change them with every event. Sedisport black was a popular choice.

It gives the chain a pretty gold color.

Titanium nitride is often used on cutting tools to increase wear resistance, but its use on chain side plates is irrelevant to this issue because the pertinent location for chain wear concern is in the pins and rollers, not the side plates.

They weren't "generic" if I remember, they were Sedisport chain purchased in big (100M?) rolls and cut to length for use. Back then, the era of 6 and 7-speed freewheels and early cassettes, the current ultra narrow, flush pins weren't needed and the specifically shaped chainrings, cogs and chain side plates were in their infancy. And yes, they were changed very often. In fact, I recall reading that during the grand tours chains were changed daily.

transfers more money into the economy, from your wallet.
so that is something..

Some BMX and singlespeed/track chains have a "golden" colour, from titanium nitride coating. Titanium nitride is very, very hard. It's a really hard mother####er, and it does help the longevity of the chain to some degree. Also, because it's a very thin coating, it's not brittle (the bulk titanium nitride is brittle, but not a thin film deposited on steel).

Two chains being equal, I would always buy the one with the nitride coating.

EDIT: of course, if the nitride coating is only on the sideplates, it has no function whatsoever.

Hey, that's quite a fun read, but this thread is not about chain lubrication.

The article sums up the most important coating on a chain. Lube on a clean chain.
The above coatings will be a worthwhile as goat poop!

I was just kidding - you know how we have those chain lube threads appearing every now and then, not leading anywhere good

I wonder if there is titanium nitrirde on the pins and rollers. Maybe there is.

Mostly not - but my KMC 710 SL does have the rollers coated, and the pins seem to be coated, too (but I have not pushed one out). I have this one box of the k710 SL, and I'm never going to buy such expensive chains again. But, as I said, all else being equal (including price), the TiN-coated chain should last some 10% longer.

But nowadays I just use the cheapest Chinese-made chains I can get my hands on, lube them well and replace them without a tear in my eye.

How much were they? I bet the Teflon coated Dura Ace 11 speed chain will be very expensive.