"Additionally the current theory is that if Venus will be sped up to below 56h per rotation it would regenerate it's intrinsic magnetic field which should be near earth levels."

That's great and all, but how exactly do we realistically speed up the rotation of a _planet_?

One of the more "probable" and more or less energy sane suggestions would be using mass drivers to eject the atmosphere at high speeds to induce spin.

The mass of the venusian atmosphere is high enough for this to actually work and still leave you a lot of atmosphere to work with, it will take 20-30 years but it still doable.

And pointing those canisters at Mars or the moon. Once you've hit Venusian escape velocity you might as well move that atmosphere somewhere else that needs it.

But compressing acidic gasses makes the corrosion problem worse, doesn't it? How do you deal with that?

Nothing says "I love you" like super-compressed canisters of acid hurtling through space at interplanetary speeds :)

I think you have a good candidate for the Portal 3 story line there.

A fleet of masses attached to solar sails imparting a little bit of momentum as each one passes by.

This is planetary engineering. It's not supposed to be fast.

Unless, of course, you are a Kardashev II civilization.

same way it actually slowed down: mess with the atmo.

Easier to live in Mars with some radiation and lower temperatures (and pressure) as opposed to 400C and acid rains of Venus

No one is suggesting living on the surface until it's terraformed, the dense atmosphere allows for easy construction of floating platforms.

As far as terraforming goes, Venus is just a better candidate for long term colonization.