WolfishMusings,
“So, I’ve been wondering if I am guilty of wasting people’s time and, if so, what can I do about it?”
A few of my thoughts:
1. When mispallelim come to shul to daven, the expectation is that kaddishes will be said, hence the brief awkward silences that occur before people realize nobody is saying kaddish and they move on. Since people have already mentally given this time to kaddish, it cannot be a waste, and you are actually preventing awkwardness by saying it.
2. I heard someone recently ask a rav a related shaila at a late maariv – the man noticed that at the shacharis and mincha minyanim, there was a fellow who would say kaddish after aleinu if there were no mourners present. He himself didn’t have a chiyuv to say kaddish but felt drawn to doing so and was wondering if it was appropriate for him to so something like that at maariv. The rav said (in a simplified retelling) that it is considered a good thing to end the davening with a kaddish, and the man was welcome to say kaddish at the end of maariv if he wanted to. And so he has ever since. So adding kaddishes enhances the tefilla b’tzibbur, certainly not a waste of time.
3. As others have pointed out, there is tremendous spiritual benefit to answer amein to a kaddish. So your question is kind of like asking, “at the end of davening I take a bag of gold coins and toss a few of them to each of the mispallelim. Am I wasting their time?”
4. I think you are well aware of #3, so is your OP meant as a subtle criticism of how people trivialize davening (e.g., that sense of relief that ripples through the room when the shaliach tzibbur starts kaddish right after chazaras hashas signaling no long tachanun)? Or is it a setup for another of your “I’m a rasha” threads?