Motz, good post above.
My concern from what I've read in this thread is how RA-Aus pilots are currently being trained. FYI, there is no special GA training for operating above 5,000'. All of Motz' points above should be taught to all pilots, especially in nav training. Is this not currently being taught?
One of my biggest concerns is the confusion on here about both airframe icing and carby icing. Is this covered in current training? If not, there are good reasons to brief it. Maybe it is taught but it doesn't really sink in because pilots might think it isn't necessary to know it?
To be honest, icing should be the least of your concerns here, because if the weather is bad enough for you to get icing VFR, you shouldn't be there. Perhaps part of the education is when to go or not go. Remember, many RA-Aus pilots don't have any time at all under the hood, and the last thing you want is to put yourself in a position with no visibility and no instrument training, flying an aircraft without TSOd instruments.
I love RA-Aus for the opportunities it gives to people, but please, if you do have plans to fly in bad weather, get the appropriate training or don't get airborne. Never underestimate the weather, it kills people more than anything else in aviation.
On hypoxia, be aware that in the USA pilots can fly along all day without oxygen at 12,500' and up to 14,000' for short periods. Maybe those Americans are fitter than us!
One thing I do think is very important in Motz's post is the engine monitoring on descent. This is taught in GA, especially in types which need a warm engine (and cowl flaps). Keep your engine warm, or it may not respond when you need it, and it can cause damage to the engine.
The traffic danger is definitely down low, close to airports. Have a look at the collision stats - they are at or near airports. I agree that pilots need to be aware of the approach profiles of higher performance aircraft and plan their frequency change in accordance with that. The higher you are, the earlier you need to monitor the CTAF, and always keep a good lookout - after all, you are in VMC.