Though not exactly on the topic of the value of staying in one ministry a long time, the below quotes from Philip Jensen are relevant.
One bad reason for shorter pastorates is a sense of ministry careerism. The minister is jumping up the ladder, so the current pastorate is only a means to an end. This will always stifle bold faithful bible preaching:
“Any preacher who would ever wish to change the church must undergo one fundamental change of heart: he must destroy any desire or ambition for personal advancement or acceptance within congregation or denomination, especially that rationalized ambition ‘that when I come to power I will be able to change things for the better’. As long as a man desires to be a bishop or a moderator, he will not be a faithful preacher of the Word of God, or a preacher who will change the church from worse to better”
If long pastorates involving unashamed teaching of the Word of God are important, then they probably require some kind of security of office. See this quote on bold preaching and tenure:
“We are not answerable to one another, or to the congregation, or even to ourselves, but to God. It is why some form of tenure is so important to faithful preaching of the gospel. The preacher who is under the authority and financial control of the denomination or of the congregation will be severely hampered in preaching the predictably unexpected message of God. It is why preachers must be willing to risk all, even sacking and imprisonment, if they are going to be faithful to preaching the gospel.”
Quotes from Phillip Jensen, Preaching that Changes the Church, in “When God’s Voice is Heard: Essays on Preaching Presented to Dick Lucas”, edited by Green and Jackman, IVP, 1995, p143.
What better gospel witness is there than a minister resigned to boldly proclaim the word of God in one place, to one people, for a long time – come what may? Is this not a beautiful ideal?