Isn't being the avatar more interesting than being the daughter of a famous industrialist?

What you also have to consider is that that's your perspective. We have to put ourselves in Mako's shoes. To us, who grew up in industrialized cultures, the whole idea of bending and the avatar is much more fascinating because it's so new and different. Even though Mako grew up in Republic City, bending has been a part of his life. Meeting the avatar, despite the fact that she's a huge deal, isn't as significant to him as meeting someone from a whole different world, the world of technology and development. This is alluding to a much more significant idea.

There's a large building theme of "old" versus "new" in this series. Benders and bending are the old ways, while industry and technology are the new ways. It's an exciting time in the Avatar world, and I believe that's one of the reasons that Amon's movement is able to garner such support. In as recently as Aang's time, it might not have, because bending was the only way. Now, there is an alternative, and people are excited about it.

So yeah, the difference in Mako's reaction is important, but probably only when it comes to setting a tone in the series, as opposed to hinting at some secret to his character.