When I double click a word in the terminal it selects more characters than I want.
There used to be a setting, but it got removed in Bug 727743 and replaced by an arbitrary, hard coded default.

My typical use case is programming and I got used to selecting identifiers with a double click. So for me the best setting was "a-zA-Z0-9_" or regex "\w". Other users may have different needs though.

I don't see any sane reason to deprive the users of the ability to configure this behaviour.

Sometimes I actually do want to include more than just word chars when I select something.

Maybe you could implement two levels of word-select. The first is reached by double-click and either selects "\w" or whatever the user configured. The second level is reached with a triple-click and selects more characters; either user-configurable or the current default. A quad-click would do what the triple-click does now, selecting lines.