Hi Reddog,
I appreciate the candour of the question. What you are really asking, I think, is what is inspiration? A good question too - are all inspirations equal?!!
The key passages would seem to be 2 Peter 1:20,21, and 2 Timothy 3:16. Both speak of inspiration, one of scripture, the other of speaking. They tell us that prophets - those given a message by God to proclaim to people on earth - do not receive their messages from humans, but from God - as they were moved by the Holy Spirit, or through inspiration ("God-breathed"). Inspiration is a useful term, for in both Hebrew and Greek, the word for spirit is the same as the word for breath (and indeed wind). Given this inderstanding, "moved by the Holy Spirit" and "God-breathed" or "by inspiration of God" effectively mean the same thing.
So in the sense of the origin of the messages, yes, the inspiration of Matthew, Mark, Luke, John, John the Baptist, Elijah, Samuel and EG White, is the same. What is not the same is the functions they were given.
Not all prophets were given the task of writing scripture - obviously. There are many named (including Elijah, John the Baptist, Samuel, Huldah, Deborah, Agabus, the 7 daughters of Philip, Elisha) whose primary task was to give God's messages to the people in their time. Some we have no record of their ever writing anything - they preached. Others wrote, but their writings were not kept under the guidance of the Holy Spirit as part of Holy Scripture. Even Paul is in this latter category for some of his writings - he mentions at least 2 letters which are not part of Scripture (to Laodiceans, and a letter to Corinthians between 1 and 2 Cor.).
Others were given the task of recording God's messages and the record of God's dealings with humankind for all time - the Scriptures. Matthew, Mark, Luke and John would be in this last category. Even the historical writers wrote under inspiration. 1 Corinthians 10:11 indicates that the stories and histories were given as examples to us - the implication is given by God - i.e. by inspiration.
That Paul's writings at least were already considered Scripture as early as 65AD is evident from Peter's statement in 2 Peter 3:15,16 - speaking of Paul's writings, he says the unstable wrest or twist them as the do "the other scriptures" which implies he considered Paul's writings scriptures too! Interesting.
Ellen White's writings, by applying the test of a prophet as outlined in scriptures, qualify her to be called inspired. She declared again and again that they were not Holy Scripture, that they were a "lesser light" to point to the Greater (the Bible). Her role was to bear reproofs, corrections, instruction in righteousness, and to confirm doctrine after others had already studied it from the Bible. In particular, she was to draw attention back to Jesus at a time when the world at large was moving ever further away from Christ.
So - inspired, in the same way the others were inspired, but like some of them, for a purpose OTHER than writing scripture.
Hope this helps - sorry I get rather long-winded.