~10% more battery life. I thought it was more, but apparently not. PWM brushed motors are pretty efficient. Brushless motors have less rotating mass, better for quickly ramping up speed or instant torque, doesn't mean much in the world of trolling motors though.
As far as noise, I'd say it's a wash. My buddy has a Force, it's definitely quiet, but not silent.
Doesn't seem at all worth it to me, my $500 Ipilot Terrova from 2009 is still working like a champ. No way could I justify $3500 on a trolling motor. Certainly seems like we've reached the point of diminishing returns with some of this new tech. You'll spend as much on electronics as you do the whole boat, outboard, and trailer.