It really is vital to do that. I had strings of 7, 7, and 9 days with only two day off in them to prepare for coming to Italy. Some of the days were very easy mind you.... maybe an hour or a little more at easy pace. Some of them were longer rides too, done mostly at endurance pace or a little above. A lot of those days I did not really feel like riding.... "oh old folks need more rest" came creeping into my head. But I was strong and felt good by the end and could have run the 9 day string on longer.

I don't think your speed is a problem. If you are really feeling bad during the ride, I think organizers will let you ride the sag wagon... easier for them than worrying about you out there struggling on the road.