Thanks everyone for your insight/thoughts. When I trained on the bike in the past, I really just looked at speed and heart rate. Over the winter, I took some spinning classes and really liked being able to see the watts as part of the workout along with the heart rate. I tracked HR and watts for various parts of the workout and liked comparing from week to week to see if I was improving.
I had thought about just getting a cadence sensor but when I looked online for various opinions, there were a few articles/comments that implied that cadence may not be all that helpful in training. While I monitor heart rate when I ride outside, at times I find it harder to judge my ride than when I did the spinning class.
Thanks again for the feedback!