If the preaching does not reflect the intent of the author it is inappropriate. If we misuse scripture to make points we believe are helpful and then point to the scripture as the authority behind our thoughts what is to prevent someone from taking Scripture and misusing it. For example, the Christian Identity Movement. I would not sit under the preaching of someone who made a practice of that sort of eisogesis. I think that the difference between teaching and preaching has much to do with motivation.
Teaching is designed to build a strong belief system or the ability to understand.
I am not comfortable with going beyond what the original authors intended and what the first century church probably understood. I think that we can use any number of examples to make our passages clear but the original meaning must be unpacked so that the hearers understand what was intended and can differentiate between the use of the example and the use of the text. To do otherwise may mislead people and cause confusion and it also allows the hijacking of scripture to make it mean things that were never intended. No eye has seen, no ear has heard, no mind has conceived what God has prepared for those who love him. The principle is the same, even if the details are not.