If your vestments were atavistic 145 years ago, what does that make them now?
Timeless and uniform. I think Theodore Parker got enough things wrong for me not to worry about what he thought. Of course, the same can be said about the following. We take our parts in turn.
In the low churches, with their emphasis on the individual and local, it isn't rare for ministers to develop an unhealthy level of prominence. How many televangelists, with eponymous ministries, can you think of? And how often, whether by tone or design, can you tell that the ministry is really about the minister? Pretty often, I'd think. In our own way, Unitarians and Universalists have done that, though today the trace of that is much thinner, but are capable of falling into it. Take Parker or Patton for instance.
Uniform vesture -- not just clerical garb of an individualist confection -- is a tool that mitigates against misplaced self-pride and affirms the unity of the ministerial college. Though I think "community" has become an overcorrective fetish in Unitarian Universalist circles, the notion that "the ministry is not about the minister" and "all ministry is interim" is about on target.
Rarely is a particular pastor the first and last one in a church. We do our part for the Gospel -- why else do we spend so much time as Unitarian Universalist talking about the "good news" and yet never quite get to the content of it; a bad omen there -- and pass away.
The ministry isn't about any one of us, even as it isn't confined to the ranks of the ordained, and customary, uniform(-ish) vesture is a lively sign of it.