Well if a tongue speaker understands what he is saying, wouldn't it be more prudent to speak in a language that everyone around could understand? I would think conveying an understandable message from God would indeed edify the speaker as much as the hearers.
You are correct, but then it would no longer be a miracle.
Why not? Isn't any message received from God a miracle? A miracle is not identified only by undiscernable jibberish. In fact that same jibberish gives the opportunity for charlatans to step in and claim the miraculous where none existed.
I think it depends on what you think happens during speaking in tongues.
If a person is "possessed" by the Holy Spirit and speaks a message in direct revelation from God, then that most certainly could be classified as a miracle...but nothing in scripture indicates that this is indeed what happens.
Speaking in tongues simply is a person speaking in a language that he did not learn before.
The message that is given could be anything, including a message the person knew all along.
Receiving a message from God may be considered a miracle, but its not how we classify it.
The prophets received direct messages from God, but we don't consider prophets performers of miracles.
Moses received the Ten Commandments from God directly, yet we do not say that Moses performed the miracle of the Ten Commandments.
You know the message of the gospel. Lets imagine you stand up in church and preach the gospel in Finnish (a language you never learned).
Then the miracle would be you speaking in Finnish and you would be speaking in tongues.
Now if you preach the same message in English, nobody would consider that a miracle.
Most people think that during speaking in tongues some attributes need to be satisfied:
1. There must be a mysterious message, something direct from God presented to the speaker in the spur of the moment.
2. There must be an unintelligible language, mystery speech.
3. The language spoken is not understood by the utterer, hence a translator should be present who makes sense of the message.
4. If no translator is present then the "feel good" element of speaking in tongues is considered the edification.
Scripture does not support these assumptions.