Hi,
I also led a mixed troop. I think the multi-level teaches the girls about sisterhood and leadership. They get to complete a lot of the patches that requires them to talk to, lead or teach a younger group right in their troop meeting.
My Junior girls have been asking to make the front of their meeting place a flower garden so we're going to make that their Bronze Award. We started them on a journey book, but realized we couldn't take our Brownies through the same journey so we're giving the Brownies Try-Its to do that tie into the journey book that the Juniors are doing. Also I couldn't start my Brownies on the Brownie Quest, because I have everything from just starting out to one who will bridging this year. I think when the younger group of girls get older will switch it up to their journey, but for right now it's too much for them.
Another issue we face is when we want to attend council programs. Some of the really great programs such as the Birthplace trip in Savannah, G.A. are grade specific so this year we decided to let the juniors pick one that will help them finish their journey and will plan a separate trip for the Brownies. Last year I incorporated all my girls in each trip and did a lot of research to attend things that weren't grade specific. It took a lot of my time and energy. I don't like excluding one group, but if they have something to look forward to next year and a special event this year. It might not be so bad.