Whether you have stock 35 watt bulbs or 100 watt bulbs, upgrading the wiring is a VERY good idea. Even a brand new XJ with stock bulbs would have brighter lights with upgraded wiring. A decade old XJ with old corroded wires can have a significant voltage drop to the bulbs. On my '96 the battery voltage with the engine running is 13.8v, while the lights are only getting 11.7v. With a 2 volt increase, any bulb will be *MUCH* brighter.