You may think that restricted caloric diets could never possibly extend people's lives as much as cryonics, but I think it is currently impossible to estimate the additional lifespan of a person successfully revived from cryonic extension. Your assumption, I'm guessing, is that this number would likely be large due to improved future technology. Once again, I think this is a huge assumption, and given the large number of things I could conceivably try.

What things could you possibly try in the present that couldn't also be used in the future on revival? There are lots of things that could theoretically be done to extend lifespans which we can't do now, but if any methods that are available now have similar effect, why shouldn't people in the future be able to apply them to at least equal effect?

Besides, measures like following a low calorie diet are not exclusive with signing up for cryonics, although having lived on a low calorie diet for about a month, I'm pretty sure I wouldn't want to live even a normal human life span on one, since it meant that immediately upon finishing each meal, my mind would become preoccupied with the prospect of the next one.