Switches and wires are cheap, plastic and insulation get brittle. I'd replace them. You don't say what battery chemistry or voltage you are using. 20 years ago 6v NiMh was pretty good but the newer receivers and servos can take advantage of higher voltages. If you are just dragging the plane out to play with a little and you were running good quality servos they are probably okay. If you are going to push the plane to its limits, then fresh servos, at least on the control surfaces, are a pretty reasonable investment. While you may not need more torque the newer servos are faster. I would be eyeballing the servo arms and linkages as well for age and forgotten wear.