I've just used the AC Delco plugs and wires. The original wires look a little nicer than the Delco spare wires but aren't really better: when removing them, I've managed to tear half of them apart: the clamp that holds onto the spark plug does that stronger than holding onto the wire itself. And no, you can't grab the end of the wire with a tool, that part is covered by the steel heatshield. The plug sockets on the wires have been coated inside with some kind of lubricant from the factory but after 10 years that lubricant seems to work more like a glue. So every time you decide to pull off a wire, make sure to have a spare to replace it.
But unless you pulled on the wires, they don't seem likely to fall apart on their own. So perhaps check the coils? (Or change the plugs and wires, and if that didn't help, check the coils). If I remember right, you can detect if a spark plug doesn't work by driving a timing light from its wire.
The right rear plug was a bit annoying but not THAT bad, nothing like the plugs on 4th-gen Camaro. It could definitely use a bit more room behind it but I can't remember anything specific, did I use a U-jointed wrench extension or just managed to insert a thin wrench head?
Here is an interesting thing: I've measured the gap on the plugs I took off, and it matches the gap on the new plugs as they come from the factory, about half the gap recommended by the manual. So why do they bother to specify the gap if they don't follow it form the factory?