I would usually. Sometimes if it's like 2 * x + b, I would not, but personally, I hate chasing down bugs like this, so just add it to remove ambiguity. Also, for like b + 2 * a, I will almost always use parentheses.
Not sure that matters when the entire language spec is expected to be part of every context window? The LLM should be capable of using the language spec to express intended precedence.