The reason change ups are suggested is so that you don't get bored. As long as you enjoy your routine and find it to be challenging I don't see any reason to change it. I go to the gym for intense cardio and strength training 3 days a week and do stretching and calisthenics on my off days. I keep the basic time schedule the same but I change up the exercises within once a month to keep things interesting as well as ramp up the difficulty. This worked for me in the past and I am hoping it works for me again. So I think all that matters is doing something that not only works for you but that you like doing so you are less likely to stop doing it.
I think if your getting the results you like and putting good effort in you should leave it go. The more you do the more you'll be able to do. I always give 100%, sometimes that is more or less depending on how I feel. As long as your not coasting I don't think it matters.
I walk outside when I can and walk or bike in the house when it rains. I do strength training 2 days a week but use the same two DVD's. I like them. Sometimes when I paint, cut grass or do large jobs that take hours and hours and lots of stair climbing I count that as exercise. I have and like my schedule but it gets mixed up just because. It seems to be working fine for me.