The only problem with the hide or spend is the Government will find a way to get it back if they have to take your house and land if they cannot garnish wages etc. My guess is the penalties that would be imposed would far outweigh any investment gains you could make on it.

Normally getting more money then expected would be a nice thing. With the government, on the other hand, I think I would be a bit stressed out until I figured out, unequivocally, that it was not a mistake and would not be taken back.