Considering my fitness tracker shows I took 121k steps in January, and the average breaths of 12 per minute, I'd have made 30k in January. 5k more than just breathing. Assuming a resting heart rate, breathing faster because of exercise is not a factor I can quantify
so it's about 20% more for walking based on those numbers.
i would definitely take the breathing! there's been too many times i couldn't walk, that's only going to increase as i age.
imagine getting in a bad car crash the day after starting the walking deal, both legs are broken. now, you are broke two ways! it's like adding insult to injury. that would be the worst feeling in the world.
when it comes down to "enough money to never need to work" vs "enough money to never need to work +20%, with extra risk if you get injured" i'll take the safe bet every time