Just to give some closure on the issue... my mechanic friend found the
problem and fixed it.  He explained it to me, and I'll attempt to
repeat it.

To help with emissions, some of the exhaust gases are re-routed back to
the cylinders.  On my engine, the outlets to cylinders #2, 3 & 4 were
all clogged with carbon.  That meant that all of the recirculated
exhaust gas was being directed straight into #1.  That messed up the
air-to-gas mixture for number 1, thus causing the misfire.

In other words, it's a valuable lesson learned.  There was nothing
mechanically wrong with #1, yet that's where the codes were pointing.

I don't regret changing the plugs and plug wires, as the motor calls
for Platinum and the mechanics recommend NGK, so I was just putting the
right plugs back in.  The plug wires were the original ones, so it
doesn't hurt to have new ones.

The car runs like a top now.

Thanks for your help.