I heard another reason for the minhag of breaking a plate. The reason was just like that breaking the plate results in something permanent, so too we wish that the shidduch should be permanent. Often we find that a brocha is accompanied with an action to solidify it. I think the inyan of breaking an object to remember the churban is only by kiddushin not just tanoim.
Accordingly, it is not neccesarily inappropriate to use a decorated hammer to break the plate. (usually, the timing of the machetenistas is off and one of them throws out her shoulder or something. The hammer is a convinience)