Is it possible to make "Look Up" appear higher in Spotlight?
You might consider Alfred for your searches. It's not only an improvement over Spotlight for local searches (using Spotlight indexes) because it learns your frequent searches, it's extremely malleable.

Here's Alfred's preference pane that shows control of searches that use OS X's built in dictionary:



Here's what it looks like to search for a word. You can set Alfred up to come up with Command/Space or you can keep Spotlight active and bring it up with an alternative like Option/Space.

In my case, I type Option/Space and the word "define" and then the word I want to define (which I've left blank here). You can see the Dictionary comes up in the search results by default because "define" triggers it:



Alfred is a spectacular product and it's quite stable and free (you do not need the Power Pack extension to look up words). I think it will solve the lookup problem and become useful to you for many other things.