What Antipitas said.
And no, it isn't customary to write them back: there's no need for you to reply to a piece of boilerplate like that letter.
If someone takes the trouble to respond, point by point, to the specific issues you raise (dream on!), then, sure, write back if you have something additional to say, but replying to a canned letter will probably just get you another one.
BUT -- just because all our reps reply with canned letters is no reason not to write to them: they do pay attention to how many people write about which issues, so it IS worthwhile -- keep up the good work.