In writing, for sure, "cela" is the correct form of "ça".But "ce" and "ça/cela" are not interchangeable because "ce" is an adjective, therefore needing a noun to complement, while "ça/cela" are pronouns, basically meaning 'this thing' or 'that thing'.
Is there any difference then between 'It goes without saying' and, say, 'Bien sûr'?
In real life, you can pick the one you prefer, depending on context. "it goes without saying", would punctuate something obvious, while "bien sûr" is just another way of simply approving (like "oui").
Please note: "ça va sans dire, mais ça va mieux en le disant"