It was absolutely the right decision and I think it was politcally- motivated grandstanding from the government to take it to the Supreme Court.
Parliament is sovereign. Yes the government does have various prerogative powers, which have a pretty broad scope in international affairs, but we entered the EU via an Act of Parliament and any use of prerogative powers that ran contrary to that act would completely undermine parliamentary sovereignity. Only parliament can undo what it has done.
Plus, its established common law that prerogative powers cannot be used to take away pre-existing rights and triggering Article 50 will ultimately lead to a loss of certain rights.
There's little to no chance or parliament voting against brexit, this is just a case of making sure leaving the EU is undertaken in line with our most basic constitutional principles.
The government was being fucking daft if it honestly thought otherwise.