In complete agreement with you. Though the faculty of speech is the highest so far, it is an evolutionary gift to mankind. Its purpose is not only to communicate and express what is within us but as a means of ascension to higher states of consciousness using the power of thought within us. It is precisely for this reason that the less we speak, the more powerful our thought tends to become. Not only does it become more powerful it develops the capacity of communicating without speech. So your understanding is quite true and there is a deeper basis to it.
However since communication is a two-way process, it requires a certain degree of receptivity for the other person to receive the unspoken communication. As yet it is very rare and hence a lack of expression is often taken as an absence of feelings. Hence it is best to speak little, speak sensibly instead of a meaningless chatter which disperses the mental energies and, to speak from the depths of the heart.
Affectionately,
Alok Da
