With the two required characteristics of an adequate measure in mind, let us examine the LDS church's ultimate measure of truth: an emotional experience.
Firstly, is an emotional experience reliable? I submit that it is sometimes reliable. Similar stimuli often trigger similar emotions. When I watch a scary movie, I usually feel something I would describe as fear. Thus, a fear response might reliably happen every time I watch a scary movie. However, feelings are very often less than reliable. For example, the same piece of music may evoke a feeling of peace or excitement at the first few hearings, but another time may cause feelings of urgency or jealousy. After dozens of hearings, the same song may even become a nuisance. Even further, the same song may cause one to feel bliss and another to feel nausea. Regarding the LDS church, while reading the Book of Mormon may evoke peace and hope at one time, it may also cause boredom, confusion, or feelings of inadequacy at others. Certainly then, an emotional experience is not very reliable.
Secondly, is an emotional experience valid? Again, I submit that it is sometimes valid. For example, if I feel valued, it is likely a result of people around me who treat me like I am important and wanted. But if I feel lucky, it does not necessarily mean that I am likely to win the lottery. If I feel peace and hope after a Sunday School lesson, it may mean that the message was full of good, hopeful things. It usually does not mean that everyone felt the same way, however. But many feel nothing, confusion, or disgust after praying about Joseph Smith's purported vision, while others report peace, comfort, joy, etc. So again, emotions are sometimes valid.
If both reliability and validity are required of an accurate measure of the truth, it seems that an emotional response is far from adequate. Just as one would not use a barometer to time a baking cake, or trust a speedometer that never rises above 5 mph., one should not base a judgment of the organization of the universe and path to eternal salvation on something as unreliable and often invalid as an emotion.