I would never sift through posted lesson plans to prepare a lesson - it is too burdensome per reward... However, there are two aspects of lesson planning in which I am constantly searching for help and inspiration: (1) object lessons and (2) historical relvance
(1) object lessons: A couple of years ago, while attending graduate school on the east coast, I taught early morning seminary. Elder Scott gave a training to all seminary teachers (Scott, R.G., 2005. To Understand and Live Truth. Talk given during An Evening with a General Authority
on Febrary 4, 2005), in which he described that object lessons can provide an anchor for the spiritual aspects of the lessons to be retained. This worked exceptionally well with my teenagers. A good object lesson is NEVER forgotten and the spiritual message is written on "the fleshy tables of [their] heart" (2 Cor. 3:3). These should be simple one-paragraph descriptions of the materials required, and the doctrinal message that is connected. Others' could post comments about variations on the object theme and impact of the lesson on various audiences. All these factors could be used to sort a large and growing catelogs of object lessons. One could search by message, audience, materials available (this was frequently my largest constraint as a student), and time requirements ... to find the perfect object lesson for the lesson. The brevity of such object lesson descriptions would make doctrine-checking simple. (The seminary teacher manual has lots of great/simple object lessons that I modified for the materials available to me, preparation time, and class needs.)
(2) historical significance: The other major bits of knowledge that I seek for during a lesson are descriptions of histories that improve one's understanding of the relevant scriptures. For example, once I taught my seminary kids about how salt was used during sacrifices in the OldT. I had them remember how they can smell a well-seasoned grill from miles away. Then we read Matt 5:13 (Ye are the salt of the earth). Then I had them envision how far away they can see a bonfire on a hill and we read Matt 5:14 (Ye are the light of the world). Then THEY taught me that Jesus was teaching about sacrifice and how His atoning sacrifice would fulfill the law of Moses. THEY then taught me how important it is to make these things known to the inhabitants of the whole earth. The little piece of history (e.g., salt used in sacrifices) made the scripture have enormous significance, relevance, and meaning.
It would be excellent to have something like http://scriptures.byu.edu
that would reference relevant object lessons and relevant historical facts to scriptures. Or, have a searchable database that is structured around topical guide themes. These could enhance lessons without detracting from the message or mixing doctrine and philosophy. I don't ever share stories unless they are my own, or historically referenced -- EVER! We should teach the scriptures and words of the prophets. I don't believe that entire
lesson plans will ever be useful.
Just some ideas...