My suggestion is that double-clicking on a word does the following:
1. the word gets selected (current behaviour)
2. produces an automatic search for that word in the current document
3. highlights all matches
I think people could benefit from this when writing important documents, where repeating a word too many times can have a negative impact on the reader. I would certainly find it useful now that I'm writing my thesis. Since English is not my first language I tend to repeat the same words over and over again.