I tend to agree with your approach. Rotors and pads are likely a waste of money and won't provide any more stopping power, with the possible exception of glazed pads, as BHD mentioned. Pull the pads and take a look.

Additionally, when the pads are out, thoroughly clean the slides with a wire brush and apply a dab of grease.

Take a check of the vacuum. If the pump output is reduced, the vacuum assist is proportionally reduced. The vehicle will still stop in the same distance, but you need more leg to do it.

Take a look at the brake hoses. But, don't replace them out of hand. Have Dad step on the pedal hard, and you feel the hose while he does this. See if you sense any bulging of the hose. If not, don't waste any money on them.

You don't have any frozen pistons in the calipers because the vehicle stops perfectly straight.

Comparing this vehicle to the SDL is an exercise in futility. Accept it for what it is and move on. It will never perform like a new vehicle, and, you don't expect it to.