There are no "wires", spark energy is transferred thru wire coil
springs that fit between the plugs and the coils.
Since this engine type came out in the late 80s, I can't recall
ever seeing them fail.

I'd recommend replacing the plugs, the boots and the plastic
housing that mounts the coils, those are the typical wear parts.

Found my own answer. Apparently this engine is a lot more sophisticated than
I had suspected. The plugs are down between the two cam towers (good
location, putting the plugs dead center in the top of the cylinder) with a
cast aluminum plate covering the valley between the cams (where the plugs
are). Mounted to the underside of that cover is a plastic box with 4 little
spark coils in a row, one for each plug, with their output aimed point-down.
Those "spark plug boots" (that cost about as much as a set of wires) sit
between the coils and the tops of the plugs and are the only connection --  
There are no "spark plug wires"!
The only problem now is that, between the boots sticking to the plugs and
the wiggling needed to get that cover out from under some wires & cables,
the old boots stayed on the plugs (instead of coming out with the coils,
where they are supposed to be held on with some plastic clips) and can't be
yanked out without some danger of ruining them. Therefore, time for new
"spark plug boots" (which will get dielectric grease on them to avoid any
future sticking) -- and that solves the need for new wires...