No, but yes.
It won't become a useful pattern, but it can be an enjoyable pattern.
Like you said, it's about exploration and surprises. If you've ever heard about the term 'easter egg' in relation to videogames (or other media) you know what this means. It's not the main goal, but it's fun for those who want to spend some extra time.
But as for usefulness, no. If you have set a goal for yourself, it should be as clear to reach as possible in the interface. Even in hidden object games you can (or should be able to, anyway) use the inventory and such without having to puzzle it out. Interface design should function, and not be mystery meat.
If you want to include things in your interface, you can start by looking at how Google does things. The search website always works the same. Enter a query, hit enter (or press 'feeling lucky') and you get your results. But they regularly swap out the logo with "doodles". Some are still images, some are animations, some are complete games. None really interfere with the actual purpose of the site.
Of course, one of the reasons google can do it because it's ubiquitous enough that people still understand the site even when it's missing the logo. Another reason is because it's a simple site. The more complex your site (or app) is, the more likely it is your easter egg will get in the way of productivity.
You have to make sure that your interaction doesn't take the place of functional interaction. But you also have to make sure that it doesn't take up empty space, so that if users click outside of a popup to cancel, they dont accidentally trigger an unexpected event. In other words, it cannot be a functional element, not a whitespace element.
Another problem is that a regular interface changes a lot. In a hidden object game you can keep clicking all over the screen and, while things will animate, you'll stay on that screen. But click any link on this website, and you'll move away. You can't (enjoyably) explore a space when every interaction with it leads you to another space. Note: there are sites that work that way (wikipedia, tvtropes) but that's a whole different story.
In short; it's a novel idea that can be put to some use... but be very, very careful with it.