I am a noob (New Rider) and recently purchased an 04' R1150RS and was initially troubled by the brakes which resulted in my performing extensive research on them. They are referred to by BMW as the EVO Braking System and were available from 2002-2006. They are often referred to as Servo brakes due to the servo that provides the power assist, it is a pump powered by the electrical system. This is where the annual maintenance comes in for to maintain the pump properly BMW strongly recommends the entire brake system be drained and all the fluid replaced to avoid wear on this expensive pump. The costs quoted for doing this annual service are in line with what I have heard.
The brakes were too effective, especially the heavier the bike in parking lots. This is especially true for LTs equipped with these brakes. If you do not finesse the front brakes at speeds below 10 mph you will jolt to a stop, even at 1 mph! With bikes weighing a lot even at 1 mph you have inertia built up and that energy has to go somewhere when the brakes say stop, which they do very well. With your tires stopped the rest of the bike keeps moving and a lot of people including me end up dropping them. I did on my first test ride, dumped it!
I still bought the bike, then had buyers remorse and was scared to use the front brakes which as you know is no good on a bike. I went back the next day and test rode a 650 without the EVO brakes, then I rode the 1150 again. This time I did some basic MSF paddle walking and braking with the front brake only and using just one finger with a lot of finesse. Took the bike out on the road after that and decided to keep her and boy am I glad. I was told in these forums 1 finger in a parking lot and up to three on the road. Given your circumstances I can see the EVO brakes working out a lot better than many other braking systems out there. I am not sure I personally would ever buy an LT with these brakes as I have heard they are worse in a gravel parking lot and with only 500 miles on the bike since delivery I have not brought myself to test them in a gravel parking lot just yet.
Try and find a bike in the 02-06' range with the EVO/Servo brakes and give it a try, but definitely keep in mind it takes no effort on the front brake below 10 mph to stop. I know use primarily the front brake all the time now, even in parking lots and approaching all stops. I only cover the rear brake to keep the habit in case of an emergency. I do use the rear brake at slow speeds when I want to stabilize the bike. I have found with BMW bikes and the Telelever front suspension that they maintain their stability better and slow speeds even when using the front brakes. Other bikes I have ridden dive a little when you hit the front brake at slow speeds and upset the suspension causing instability. The BMW not so much.
Overall, I love this bike. Not sure if I am up to the task of changing the brake fluid, bt will definitely get it done annually. Peace, -D