I usually process a bunch of vegetables in a Vitamix because I think it's better to have it with the fiber. Would this be less of a good thing than just a straight juice? I've heard the juice loan isn't great without the fiber, but I don't know.
Blending a nice way to eat some vegetables for sure.
The idea of this temporary diet is to give your body time to live off only vegetables, with limited digestion effort. Even if you don't care about digestion, it is hard to eat, even blended, enough vegetables to maintain energy/calories/body weight. Even blended, I don't think you could eat 10 lbs a day for 90 days. That's the main benefit.
Unless you have an actual major sugar problem, I wouldn't worry too much about the sugar spike from juicing. We do much worse things than that to our body. Heck, some people even drink alcohol.