To be frank, when departing MEL, I find the Express Card more valuable than my APEC card because without the Express card, they will still weigh your carry on, with it, they don't bother. Also, the APEC card does not get you though the security checkpoint any faster, whereas the Express Card does. At least that was the case with the old setup - I haven't tried going through with just my APEC card through the new layout yet.
OK interesting, the hand luggage piece is not a problem for me, as my travel is invariably MEL-SIN, and I just don't bother with carry on to Changi even if I travelled down to MEL with only carry on. And as someone who usually "cuts it fine" (ie arriving at airport at around 65 mins before departure) unless there are a lot of later flights leaving, I usually breeze through security and immigration, the more diligent passengers are already well through before I get there.