Visitors? Do you mean the saved or the unsaved? For the saved I would pray for more exigetical preaching that taught us in ever deeper ways whom God is and what our relationship with Him should be like. It seems our church has a 15 min sermon limit. I think we should be lead by the Spirit when it comes to sermon length. For the unsaved I would pray for more preaching on His law. Gal 3:24 (NASB) "Therefore the Law has become our tutor to lead us to Christ, so that we may be justified by faith."
The 15 minute sermons are something my present church does not do. Our service typically lasts at least an hour and a half and frequently the Pastor will deviate from the bulletin because he feels God is calling him in a different direction. I have to admit that this was a little hard for me to get used to as I grew up in a church that had the 15 minute sermons and everyone expected to get out exactly at 12:00 and be off. But I really do need the sermons because I stray off the path more often than I would like to admit and they help to get me centered again.