Is this something the universe can work with, or is it too vague?

There seems to be an underlying assumption in your question that your requests are creating your reality. Therefore, according to this assumption, you have to be precise in your requests to ensure that what you create is exactly what you want.

None of this is true :)

You are actually writing your requests to get the feeling of "hands in the clay" as regards your life. You are writing them to have fun writing them because you are a creator and creators have fun when they are...creating :)

Take a look at the following answers for more information about this:

• The better you become at manifesting your desires, the less you have to 'forget about them'?
  
  
• How does one focus one's attention on one's goal while simultaneously surrendering one's attachment to that vision?

So if you were to write a one line request..."I want to have a great life"...and stick that in your box, it would work also :)

If you were to not write any requests whatsoever and just Get Happy, that would work also :)

Stuff manifests into your life whether you write requests or not. Otherwise, if you think about it, people who don't visit Inward Quest and learn about these ideas wouldn't ever get anything they want in life :) But people are getting what they want around the world all the time regardless of whether they understand these ideas or not...because it's an automatic process.

But it's not satisfying when you don't feel you have had a part to play in your stuff coming. It all feels random and distant when stuff just appears out of nowhere, even if it is "good" stuff. And often you don't even recognize that what came is what you asked for because it comes as blended manifestations.

So all these requests are about are to give you the feeling of being involved in the creation of your life...because that's where the thrill of living comes from...not being a passive observer of things happening...but an active participant in the game.

With that in mind, you write the request that makes you feel the best about what you want. In that way, when the stuff comes, you'll be more lined up with the vibration of it (because you've "softened" your resistance in the direction of it) and you'll feel like you were responsible in some way for it coming.

I know if you have an analytical type of mind, this kind of answer is immensely frustrating when you hear it for the first time.

I know that because I (sometimes) have an analytical type of mind :)

In fact, many people it seems don't want to hear that life is good automatically if they take the trouble to stay feeling-good.

Many would rather believe that their prayers, affirmations, visualizations, goal-setting statements, or whatever, are actually important to them getting what they want...and they invent all sorts of creative reasons why stuff comes or doesn't come, often crystallizing them into rigid systems of belief and behavior...but that's fine also...you can play the game of life in many ways.

It's not how you play the game that's important, it's how much fun you have while playing it :)