If you don't mind I will analyse what you just wrote:
"One big advantage the BMW has over Lexus is that there are independent specialists in this area"
Basically the reason for this is because it is not financially viable to be a Lexus independent specialist because they do not break often enough to earn an honest crust. The reason why there are an abundance of BMW specialists is because there are an abundance of knackered BMWs needing to be fixed
And for any smart arse who comes up with a comeback saying there are no independent Rover Montego specialists in their area is this because they are reliable too ............... Just don't :P
Stick with the Lexus ............... you know it makes sense