Well, I can give you some useful information that people often fail to cover when learning languages. There are two main components to learning a language in the modern world:
- Fluency (listening comprehension and speaking)
- Literacy (reading and writing)
The definition of fluency commonly includes literacy, but in actual real world use they are separate things. There are people that can speak a language fluently, but are fairly illiterate. People wouldn’t tell them that they aren’t fluent though, because their speaking and listening comprehension are just fine. The trap that a lot of language learners fall in is the opposite situation: they become literate, but they lack fluency.
How does literacy and fluency impact each other? Well, fluency requires a subconscious competence of a language’s fundamental rules. When listening and speaking, grammatical patterns have to be recognized and produced in near realtime. You don’t have a lot of time to stop and translate. Practicing speaking and listening will therefore lead to a greater mastery of the language. On the other hand, with reading and writing, you can pretty much go as slow as you want, taking the time to translate things from your mother tongue to the target language. People can get reasonably fast at this, but it alone generally will not increase your mastery to the level needed for fluent communication.
THAT SAID, reading aloud is a great way to practice speaking and developing the muscle memory necessary to produce the correct sounds at speed. Literacy definitely can help with your speech as well as other supporting elements like rehearsing grammatical patterns that you don’t use often, and reinforcing vocabulary.
TL;DR Speaking and listening require greater mastery of the language and increases your ability to subconsciously understand Japanese. It is the fundamental element you learned your mother tongue with. Literacy is good for supporting your language learning, and it also benefits from your speaking and listening practice.