I think it is worth if there is enough search volume. I use Google insights this way:
I picked two terms that are searched for all over the world ("css menu" and "css menus"). These two terms create a nice gap and I want the search volume of the target term to fit between this gap. I write these two terms on second and third places. On the top box I write the term I want to compare.
Check this link for "opal", your username.
Google Insights for Search