I think the Australian 1c and 2c pieces are closer to brass than bronze (Composition: 97% Copper - 2.5% Zinc - 0.5% Tin) but you are correct it is not pure copper stacking. Im stacking these due to their melt value being higher than their face value.
I have mixed feelings about this...
It is also true that for a while the cost of the metals in 5 cent coins was pretty much close to the melt value so I was considered stacking 5 cent coins. However, refining the copper or nickle out of the coins is not a trivial matter and the expense would make it unfeasible. That particular alloy is just one of many cupro-nickle alloys and doesn't seem to have a lot of other uses outside of coins. I am sure when the coins are replaced with a cheaper metal or just taken out of circulation the mint will be able to melt them down to make different coins but beyond that I can't think of anyone who would want that type of alloy.
Over in the USA they have made it illegal to melt down copper cents to sell, nothing to stop the Australians trying that as well, I doubt it would be successful as you can make a smelter in your backyard and use your barbecue gas to run it.
I know that junk silver coins are valued according to their silver content, and the cost of the other metals is not usually included in the price. So pretty much in a 50% silver predecimal coin you are getting half the coin for free. There is never any consideration of refining the silver out of the coin as it is far easier to just sell it in its current form as it is for 'investment' use and not industrial use.
However copper is not usually considered to be an investment metal, its value is in its usefulness. So if you wanted to have it in a usable form, you would probably need to refine it before you sell it, unless this particular alloy is commonly used for other items.
The only market I can see for these coins would be other people speculating that the value of old bronze/brass coins is going to increase to the point where they become worthwhile investments and they want to get in before bronze/brass goes to the moon.
The other market would be refiners and they will obviously charge for the service or buy coins at a lower value. There are plenty of other sources of scrap copper with fewer impurities which would be preferable to refiners.
I looked into taking my 50% silver coins to a refiners and they wouldn't even consider taking less than 100kg in a consignment, not worth their while to process less than that and they didn't want to store it waiting for it to get to the required weight. They would however accept any number of 1966 80% 50 cent coins or gold coins.
They (Copper/Brass/Bronze coins) are tempting because they are in plentiful supply, I can lay my hands on kilos of the things with a few phonecalls, and they are cheap. However the space they take up, the smell, the likelihood of corrosion and the limited market for resale has prevented me so far. I would rather stack junk silver coins. Both have similar issues but on balance, I think the case for the silver coins is better.
On the issue of stacking pure copper I have no disagreement, I wanted a big shiny copper ingot but the premiums were ridiculous, I am stripping old wires and collecting scrap copper to make my own, one day, after I finish all my other projects..