Have you considered replacing immediate jolts with slower jolts? Just as your brain is ready to get serotonin flowing from exercise, it is also programmed to get it from eating (and cooking), and from hanging out with your children. Using these sources of longer-term positive reinforcement may also have positive feedback in improving your wife's afternoon, which may start an overall positive feedback loop in your family life.

Also, you mentioned that you dislike noise. You may want to look into Sensory Integration Disorder - even if you have a mild case, some common coping strategies may improve your life and reduce your need for decompression time after work.

Oh, for me it does. I feel an enormous mood lift from a bit of exercise, especially if it takes place outside on a sunny day, and it kicks in pretty quickly. I agree walking may be not quite intense enough to get much of an effect (though I think it does a bit, for me), but I cycle to and from work (not fast or anything; it's a short distance, though a tiny bit hilly, and I'm a very casual cyclist) and that does give me a little boost most days, and some mental space between work and whatever's next. Of course, it sucks in horrible weather.