Fuji Abound
all good points, especially#7. This is one thing you can easily do to a) make yourself more visible and (b) increase by quite a lot the chances of seeing another aircraft that was on a collision course.
Realistically, transponder on in D or G airspace will improve things in an area of radar cover, where a controller is providing a radar service to an IFR flight, you will likely be called as traffic information if a threat (ie likely to pass within 3nm). The more likely hazard is from VFR aircraft that happen to be on a "line of constant bearing" (read=collision course) and don't move across the windscreen. Very hard to spot. Especially gliders. This is why turns are useful.
Benhur, absolutely. Anything that increases the time you have to spot closing traffic has to improve the odds.
2 Cessnas collided over Milford Sound a few years ago on a tourist scenic. They were almost parallel but slightly converging. (This is a high density area) The report found that although one of the passengers could see the other aircraft approaching, and even photographed it, it was unlikely the PIC would have seen it without some unusual contortion. The other pilot's view was likely to be obscured by the wing.
So, yeah, big sky, but hey! In my opinion this is one area of flight safety where the unexpected will kill you. (mind you, I'm an ATCO, hence -in part-that opinion). Engine failure? Rare, and trained for. Fire? Very rare. Bad weather? Too common, but you have the answer in your own hands. Structural failure? Horrid but extremely rare. Stall? Too common, but still, trained for. Collision? Ride it down.
Keep things turning. (heads and aircraft.)