Hi Kitteh,
As someone learning Japanese as part of a two-term accelerated course at a university level and is using WankiKani to memorize kanji, hiragana and katakana are prerequisites to learning kanji and spoken Japanese. Full stop. All the pre-course work I had to do was “know how to read, write, and say hiragana and katakana,” and all the sounds and readings of kanji are based on hiragana.
Even if you choose to never try memorizing kanji after today, you should at least learn hiragana and katakana if you want to learn to speak Japanese. Romaji – the Roman versions of the words – doesn’t quite convey the sounds your mouth is supposed to be making. (Quite literally, I had a friend ask me a few minutes ago why certain vowel sounds were “silent” and I replied, “Because you’re reading the romaji incorrectly, just as I used to.”) As well, you may never quite understand how grammar conjugation works without at least hiragana. Katakana is for borrowed words, and they will always be written in katakana, so that’s often useful for learning, in my opinion.
With that said, after 6 months of learning, kanji is becoming increasingly more important to my understanding of grammar. Since a lot of words can be written with the same hiragana, I’m running into similar situations an English language student might encounter, where I’m looking at a bunch of hiragana and wondering, “There’s at least five different words I can form using this collection of characters… which one is it?” and I find myself thinking that just having the kanji would be easier to read, even if I have to go look it up. I’m not chasing the Level 60 cake. I just want to communicate better.
Hope this helps, and best of luck.