I agree with you. My locos that don't have sound decoders yet aren't used much anymore. DCC was a great first step for independent control of trains without constant block power switching. But, DCC control of lights and sounds on the trains really brings them to life. My RR had its dormant times, but hasn't since I equipped my first loco with a sound decoder.. Like you, I put them in my old locos myself.
I've just gotten into adjusting the sound levels with JMRI and programming on the main. It takes all the drudgery out of adjustments. I bought a sound level meter recently. I hope it will help me adjust the various sound levels to be more consistent and appropriate across my "fleet" of about a dozen steam locos and half as many diesels.