Another idea I've always thought would be a good one for the UU is to add some liturgical flair. Just because the UU is very open and diverse theologically doesn't mean they can't have a liturgy like a Roman Catholic or Episcopalian parish would, but, in practice, they usually don't.
For example, many Christians churches have liturgical seasons that correspond to certain themes and colors. For example, for 40-45 days starting with Ash Wednesday and leading into Easter, there is a time period called Lent where all the clothes and decorations at the altar are purple, and the priests or ministers dress in purple robes. Then there's about 7 weeks of Easter, where everything is white and gold. Every day of the year is part of some liturgical season.
What if the UU did something similar, but taking themes from nature? From Memorial Day to Labor Day, the ministers could be dressed and the churches could be decorated in yellow for summer and the sun. After Labor Day through the end of November, brown for fall. December 1 through the end of February, white for winter. March 1-Memorial Day, green for spring. I'm giving traditional cultural and climatological dates for the season changes, but the equinoxes could be used as well.
There could even be general themes to the services during each season. Maybe environment and nature during spring with the green, etc..
Also, things like incense could be used. Young adults love incense these days.
Give the services more of a sense of timelessness and mystery, like the ancient pagan temples or the Catholic mass or whatever.
Have a set order of services that's consistent from week to week with set wording and call and response ala the Christian with some mysterious wording. Add some Latin, Hebrew, whatever. What's that universal language people tried to make up and implement a century or two ago? That could be used. Whatever.
It's just personal preference, but I like to have a little bit of a sense of mystery and timelessness and changing of the seasons and familiarity of liturgy with my religious-type stuff.