Regarding your second question about a slightly poor idle, many things could cause this.
I don't think the wires have a high failure rate. The original wires (if yours are original) are made of solid copper (not a copper / silicon blend) and are fairly expensive, as far as wires go, and seem to last quite a long time. There is no replacement interval for spark plug wires.
What people usually do is replace the resistor boots or ends of the wires, and they are about $7.00 each. You can check these connectors for intermittent short circuit.
Regarding your spark plugs, make sure they are the original copper core, non-resistor type. Also, the gap might be too small. Check to see that the gap is 0.8 mm (.032 in.).
If you have no record of replacement of the cap and rotor, it won't hurt to change these with the plugs. They are cheap and easy to do for a DIY'er.
I don't know if it'll fix your slight miss at idle, though.
How does your car run when cold at start up? You could also have a problem with your EGR system.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".