As it happens, another national Unitarian entity went through a similar branding process a few years ago, and we might learn from their experience. I'm referring to the General Assembly of Unitarian and Free Christian Churches, commonly known as the British Unitarians.
Back in 2007, the British Unitarians adopted a common visual identity, along with a new national website. That website (archived link), for reasons best known to them, seemed to treat the color palate as a challenge rather than a set of options: even now it makes my head hurt. It has since been replaced, and so I thought the branding exercise was a failure.
But it wasn't, surely due in large part to DUWIT -- "Development of Unitarian websites and IT" -- whose DIY web management system has some of the design elements baked in. To riff on an old Unitarian joke, these sites have one color theme at most; also, their revised chalice logo was a much less radical change from those popular in the 1970s and 1980s. Most British Unitarian sites use this system, which makes appropriately-scaled brochureware (opposite of interactive) sites. But even custom sites often contain the logo or tag/strapline, and most stay on message. Two good examples of this later case are the Cheltenham & Gloucester Unitarians and the Brighton Unitarians.
So where can you find out more about this standard? Download this PDF.
And I expect --- or rather, hope -- the UUA will release an identity standard of comparable scope, of which the logo is a part. (If so, I think making the color palate, typography and wordmark the teaser would have been less, um, shocking.)
As it happens, I've been following denominational identity standards for years and you can look at the British Methodists (290,000 members) and the Mennonite Church USA (110,000 members) for comparison, by communions of the same scale.
I'm not saying that particular Unitarian Universalist congregations and groups should follow a common standard, but -- like a style guide -- each congregation should have a standard. Write one, subject to your congregation's decision-making systems. (The UUA should, of course, follow its own.) That would go far to keep every change on the church site from being an exercize in head-scratching and complaint, and improve the appearance and usability of your print and web communications.