I just changed my wires at 10+ years and 90K miles. No signs of trouble but the wires are clearly the weakest link in the 3.4 crossover ignition system. For $50 or so I felt it was reasonable preventive maintenance - at that age time takes over mileage as a wear-out metric, the insulators and conductors in the wires could easily degrade to the point of loss of spark energy. The OEM set is a harness that includes all clips, hangers, etc. and will keep the wires in the proper places away from hot spots, etc.

Jeff
96 T100 SR5 4WD Ext Cab, Warn Hubs, HD torsion bars, Bilsteins, Camper Shell, TJM bar, factory 31 x 10.5's, Powertrax No-slip rear, Recaro driver's bucket