Is wearing of a clerical collar becoming more acceptable? I hope so. I never had a WELS pastor yet that wouldn't be fit to wear one. I have loved all my WELS pastors - best pastors on the planet. And my pastor came to church wearing one for the first time. He said it gives him more opportunity to talk about Jesus to strangers.
I do not know if I can point to any kind of trend developing in our synod.
The wearing of clerical collars fits into the category of adiaphora: those things that God has neither commanded nor forbidden. While wearing a clerical collar might more commonly be associated with clergy of other denominations, it is an option for clergy of our church body.
As you indicated, and as the term suggests, a clerical collar identifies a person as a member of the clergy. That identification can open doors for conversations about the faith.
As it is with any change in congregational life, pastors will do well to speak to their members about the rationale behind their use of a clerical collar. Such conversations can address any misunderstandings that might exist.
Thank you for your kind words about our pastors. I hope many of them read your words.