I'm one of those commuters that also does long hard rides on the weekends and races. I have a professional coach. Coach's approach to rest is to have a recovery day after any workout that includes high-intensity intervals. That recovery day can be either no riding, or an easy commute: short route and at recovery pace (HR zone 1; 15-18mph). My total recovery days are Friday and Sunday, as my hardest workout is generally on Saturday. I'll do a fast group ride Sat, and then typically add base miles to get up to 75-80 miles. My commutes range from 8 miles to 20 miles one way, depending on what type of workout I'm doing on the way in to work.

To build muscle, you need to stress the muscle then rest it. The growth happens when you are resting. No rest = no growth. The harder you stress it, the more recovery time you need. If I was only doing base miles, I could ride every day, as the night's rest would be sufficient. Taking muscles to the point of failure, however, dictates a recovery day.