I allways use panning and stereo for live playback. Is it perfect - no. Is it better than mono - yes. Does it do any harm - not in my oppinion. I also frequently listen to my tracks in the car for learning purposes. I played a gig last weekend with terrible sound for me but most of the tables were seated for great sound during dinner. Tracks and vocals were were about 30 feet apart with stereo piano and guitar in the middle. Since most of the tracks were just bass and drums they were panned to the center. When a string part or brass section came in it made it sound more realistic - like a live band.

I have heard fine symphony orchestras that sound great with perfect seating back about 40 rows and not so good the next night when the seats are less than ideal.

Make your tracks sound as good as you can and realize live perfromance is allways impacted by the accoustical environemnt you perform in.