IMO the only things to worry about when having an expensive bike as your main commuter is having to worry more about theft and getting more stressed about the bike getting filthy. If you're not the kind of person to take careful care of your drivetrain, even a bike with 105/Ultegra is going to be trashed if neglected during a rainy winter of commutes. So in that sense having a cheaper bike can be less stressful.

Scott