I have a bunch of these I got from the Easter Show as a kid. 1996 Parkes, 1997 Kingsford Smith, 1998 Florey, 1999 Anzacs, 2000 HMAS Sydney. They are all S Mark, plus I also have a C Mark Florey. I notice there seems to be a flood on Ebay. So I guess it is unlikely to get good value or even a sale on there. Plus at $12 thru to $25 in value (depending on year), I guess the fees wouldn't make it worthwhile. Is there any real reason to hold these? I am thinking of doing so because of the above reasons, rather than any true desire to do so.
I think you are right, keep them because they mean something not of the value. The one you do want is the Victoria Cross one, that can go $200+ also people like the 2007 PNC Mob of Roos. The rest are general like you said. The Military ones generally seem more popular. Wait until our currency changes again, then the value will increase.
The ones from the Easter Show, were they the "Mint Your Own" Coins where you pressed a button and it stamped the "S" into the coin? They are rarer than the normal versions of the coin and usually go for a bit more but you still have to find someone to sell them to. I haven't got a copy of the latest guide but they would be worth holding onto, better than spending them for $1.
They are in the little sleeve/cards and I think it was the stamp your own (hard to remember) I notice on ebay the HMAS Sydney and Anzac seem to be going for $25 or so. The others $10-$15. I figure the coin store would pay less than that so they can on sell at that price.