I'm like you in terms of self description and goals. I'll never race (56 years old) but love riding and like to know how I'm doing. Got a Stages power meter, and I'm enjoying it. I suppose if I obsessively compared myself to more serious cyclists, I might get discouraged. But I compare myself to myself. That said, intervals are both necessary and sufficient for improving, assuming you haven't started them. I don't interval until puking, but I do push myself. And have gotten faster. In any case, power meter is useful in all this. But next bike will probably have electronic shifting too.