While that is the conventional wisdom, I ride by heart rate to "monitor" my intensity. I picked/found a heart rate that I want to ride at and stick to that... Doing so this year, I've increased my cadence (from under 70 to high 80s/low 90s), speed (from 8-10 mph to 14-16mph over 50 mile+ rides) and endurance (from whining abut 10 mile rides to completing a 600km ride under max allowable time).

Obviously YMMV.

But, to the OP's question, yes, rest days are beneficial. But as others have noted, rest doesn't mean no riding....just not intense effort riding.