Speed matters in every position. It's a key discriminator when you're comparing ostensibly similar players.Not true. He was just better that season. He still had bad performances that season, but he had a lot more great performances in 2013-14 than last year. Even if the players around him had a better season than their actual seasons, Januzaj would have still shown brilliantly.
Januzaj doesn't need more speed unless United want him to be a pacey winger, which is just not the kind of player he is.