This question has so many potential answers. How often should you take a rest day? Well, that depends on how you're feeling day to day, how slow/fast you do your recovery runs, if you're injured, sick or healthy.
I found when I ran faster on my easy days (6:00-7:00 pace) and when I killed my workouts, I needed rest days or I would "burn out" (while running 50-70 mpw)
As I slowed my easy days to 7:00-7:30 pace (generally... sometimes slower, rarely faster), increased my mileage dramatically (90-100) and ran more within myself on workouts, I almost never need a day off now.
So it totally depends. I think it takes a long time to learn and experiment with this to get it right for yourself... but I am a big proponent of less days off, more mileage and dramatically slower easy days when you are supposed to be recovering.
Once a week (usually every Monday) I will have a day where I run whatever I run at 8:00 pace (maybe 4&8, 6&6, 5&7, or just 7 or 8 with no double). This seems to work for me as a recovery day and is certainly better then a day off every week.
Like you, I also take 2 weeks off in spring and fall, and I also will take a day off here and there if I'm very sick (maybe once a year), peaking, or if life gets in the way (rarely, but does happen).
Somewhat related... I have found that the best approach to getting better is to run as much mileage as you can at a slow pace, and then have the pace come down as you get fitter, rather then run fast for lower mileage, and then bring up the mileage but at the same training pace.
i.e. rather then run 50 mpw at 6:30 pace and then add 10 mpw every month, but keep running 6:30 pace, run 100 mpw at 8:00 pace and let the pace drop naturally over time to whatever your now increased fitness allows it to.
Amazing that it took me years of training and listening to guys like Malmo to realize this.