Dear Yong Peng;
You wrote: "My opinion is we should first look at other sutta passages, and only when they are exhausted that we begin to look beyond the suttas. For example, you provided an excellent write-up on 'dhamma', a word which may occur several times in the same sutta taking on different meanings with a difficult context."
But most if not all of the Suttas have already been translated into English, not so for most of the commentaries which are an important part of Theravadan lineages of Buddhism. (Following up references in the Pali Dictionary of Proper Names makes this very apparent with most of the historical detail provided by the commentaries.)
So commentary translation in some ways provides provides more value, rendering in English what does not exist yet in ENglish and is not yet accessible.
In fact, Bhikkhu Bodhi's first translation project was a sutta and its commentary:
"At the end of 1975, I moved to Kandy to live with Ven. Nyanaponika. He had seen some of my personal translations and suggested I translate the Brahmajala Sutta (the first sutta in the Digha Nikaya) with its commentary and subcommentaries. The resulting work, which commenced my "career" as a translator, was published as The Discourse on the All-Embracing Net of Views (1978)."
http://www.inquiringmind.com/Articles/Translator.html
He goes on to comment on the relation of commentaries to suttas:
"To understand what the commentaries are doing at the doctrinal level, we have to remember that the suttas themselves are not uniquely Theravada texts. They are the Theravadin transmission of a class of scriptures common to all the early Buddhist schools, each of which must have had its own way of interpreting them. The commentaries that come to us from Buddhaghosa (and others) take up the task of interpreting these texts from the standpoint of the Theravada school. Their view is thus necessarily narrower than that of the suttas because it is more specific: they view the thought-world of the suttas through the lens of the methods of exegesis developed by the early Theravadin teachers, using these methods to explicate and elaborate upon the early teachings.
If we compare the suttas to a vast expanse of open territory, reconnoitered from above as to the main features of its topography but with its details only lightly sketched, then we might compare the commentaries to a detailed account of the lay of the land."
Thus commentaries seem indispensable to the suttas and Theravadan Buddhism.
With metta,
Jon Fernquest