I wish I had a good info for you, Paul. Here is my take. I am a little younger and had a bad accident on the bike about a year ago. It seems to me that consistency is the most important training attribute as we age. It isn't that we cannot improve a bit, just that it takes so much longer to improve than when we were younger. I still have not gotten completely back to where I was but am not giving up. What has helped me is patience and making sure I am recovered well before any hard workouts. I also think it is important to go really hard once in a while and even to sprint hard now and then. How often? For me, nowhere near as often as when I was younger.
Interestingly, I have not been using a power meter for the past several weeks because the new bike does not have one. Drives me crazy.