Unfortunately for me, the question has become somewhat moot as our branch will be undergoing some changes in a few weeks.
Back to the original topic. After seeing post #3 by rpyne, I turned to the CHI to study more about the YSA Committee. Reading about the role of the committee, I believe that it could be the ideal vehicle for coordinating activities in a YSA unit. It meets as needed to plan service, leadership, gospel learning, fellowshipping, and social activities. Sounds like our activities committee. It includes a member of the bishopric, Elders Quorum counselor, Relief Society counselor, adult advisors (probably not needed in a YSA unit), and the YSA leaders. The role of YSA leader could easily be filled by what we used to call the Activities Committee Chairperson, who could also be responsible for developing annual budget requests. The only real change is that there aren't any Activities Committee Specialists. That could be filled by asking unit members to help on the ad hoc basis suggested by others in this thread.
Again I thank you all for the input. It has been very educational and I'm sure that others who find themselves working with this very special group of members will find some good insight. I'm not going away - I will have some big questions as we transition and I hope that I can continue to contribute in some meaningful way.