Maybe I've been lucky but (touch wood) I have had surprisingly few wiring problems in recent times; on the other hand maybe it is the fact that I had every imaginable problem years ago and there is now a load of extra corrosion protection I usually include when assembling everything....
the SON coax connections are fine and dandy but they lack one ingredient that I favour; easy bodgeability.
Agreed, but on the other hand, the only wiring that's ever given me trouble has been a run of figure-of-8 stuff to a rear light, and that technically still works (it's just looking a bit fugly since I re-made some connections in a hurry after it got snagged in a bike parking incident). All my SON coax has been utterly reliable, I reckon because its greater flexibility makes it less inclined to form loops that can snag on things as cable-ties slide around, though a frame with internal cable routing certainly helps.
It probably helps that I know how (and have the equipment to) make such connections properly, and tend to be fanatical about strain relief, particularly of trailing cables where they enter lights - if that breaks, you're stuffed.
TBH, the main barrier to bodgability isn't the cable, so much as the connectors. Break the cable off a spade connector, and there's not much you can do about it other than remove the heatshrink and twist and tape wire round the remains, or attempt to use the spade to clamp bare wire against the terminal. I'd classify both of those as type-2 fun. At least those lego-brick things can be re-terminated at the roadside. The main thing is to have enough slack to work with. Or a length of pre-terminated cable in your bodging kit...
In terms of what's actually failed on my dynamo lighting setups it mostly seems to be the lights that cuase problems. I've had:
1) The snagged cable mentioned above. (Had to re-route to gain slack and fit a new spade connector.)
2) Cyo break at the plastic moulding where it bolts to the bracket. (Upgraded to an IQ-X.)
3) The internal wiring between the two halves of a 4DToplight Multi shear at a soldered joint while changing the batteries. (Trivially easy to repair with a soldering iron).
4) Loose spade connector fall off the back of a 4DToplight Multi while faffing with luggage. (Tightened the spade with pliers and re-connected.)
5) The switch ring on the back of a Cyo crack in two when I rear-ended a Range Rover due to incompetent use of freshly-oiled rim brakes. (Fortunately I'd kept the broken Cyo from (2) in case it came in useful and was able to swap it over.)