Hello all - I've updated my TidyTabs plugin to include ST3 support.
TidyTabs allows you to close old tabs via a keyboard shortcut (ctrl-alt-w by default). You can also set it up to automatically run each time a file is saved. New in the latest update is a "threshold" setting, which only closes tabs if there are more than a certain number in each view.
You can install via Package Control. More info here.