Personally, I think this sentence would benefit from a comma before the ‘or’. And in that case we could probably benefit from a clearer way of setting aside the parenthetical.

“Sometimes writing for money, rather than for art, or pleasure, is really quite enjoyable.”

– this seems awkward to me. This version, though:

“Sometimes writing for money—rather than for art, or pleasure—is really quite enjoyable.”

Isn’t that more fluid?