Machining is definatley worth it.:uh-huh:
Shuddering usually means warped discs. If your discs look worn then get them done.
It's like a tetanus shot: If you can't remember the last time you had it done then it's due (same for bleeding the brakes ).
strutto - the amount removed from the disc is dependant on how deep the grooves are. The machining takes them back to a flat surface.