Show me a campaign law that was broken doing this and I'll consider it a valid point. As it is, a candidate who does this to get my attention is probably a candidate I will likely pay attention to. If their message ends up sucking and I dont like their policies, I throw it in the trash and move on with my life.
End of the day, politics is a numbers game and moralizing over the typeface of a letter that at worst ends up in the junk heap is the last thing worth even an iota of energy getting comparatively upset about.
If someone feels so strongly about slick typeface maneuvers to get voters opening an envelope, I'd encourage that person to run for office themselves and make outlawing that sort of activity a campaign promise and let us know how it goes.