Some good articles showing that:
1. Meditation does indeed increase parasympathetic activity
2. Non-directive meditation is better for relaxation, as compared to "concentration meditation"
The reason that non-directive meditation seems to work better is that "concentration meditation", where you try hard to maintain a mantra or focus on a candle working hard to stop thoughts can actually build stress since it is just something else for us Type-A folks to try and control.
If you try to control anything, it just builds tension. The key is to be aware of thoughts but don't get caught up in them.