"This is sometimes known as the Keynesian ratchet. Boost spending in the good times, then argue vociferously that it cannot be cut in the bad. Because cutting spending in the bad is austerity and that's doubleplusungood. And thus does the size of government ever ratchet up which is the point and purpose of the tactic.
OK, that last is me being even more cynical than usual."
More cynical and partisan than usual anyway.
I'm sure you know perfectly well that's not what Keynes proposed. He said "save (or pay down debt, which is a kind of saving) in good times, spend (even if you have to borrow) in bad times... " which is essentially what you're proposing. The fact that governments (especially Tory governments, thank you) typically do only one side, the other side, or neither side of this and then mess up badly doesn't really discount Keynes' model.