TileView tile border width

Hello Simon,
As for the issues with clipping a bottom tile and the e.Item argument set to null, this behavior is unexpected, an we need additional time to research it. I've created separate tickets on your behalf (TileView - The bottom tile is clipped, TileView.ItemCustomize - The e.Item argument is null on the application startup) and passed them to our developers. Please stay tuned. We'll update those threads as soon as we make any progress.
As for increasing the border width, this task is a bit complicated and requires creating a TileView descendant. Here is the code:

C#
[ToolboxItem(true)]  
    public class MyGridControl : GridControl {  

        protected override BaseView CreateDefaultView() {  
            return CreateView("MyTileView");  
        }  
        protected override void RegisterAvailableViewsCore(InfoCollection collection) {  
            base.RegisterAvailableViewsCore(collection);  
            collection.Add(new MyTileViewInfoRegistrator());  
        }  
    }  

    public class MyTileView : TileView {  
        public MyTileView() {  

        }  
        protected override string ViewName { get { return "MyTileView"; } }  
    }  

    public class MyTileViewInfoRegistrator : TileViewInfoRegistrator {  
        public override string ViewName { get { return "MyTileView"; } }  
        public override BaseView CreateView(GridControl grid) { return new MyTileView(); }  
        public override BaseViewInfo CreateViewInfo(BaseView view) { return new MyTileViewInfo(view as MyTileView); }  
    }  

    public class MyTileViewInfo : TileViewInfo {  
        public MyTileViewInfo(TileView view)  
            : base(view) {  

        }  

        protected override TileViewInfoCore CreateViewInfoCore() {  
            return new MyTileViewInfoCore(this, View as TileView);  
        }  
    }  

    public class MyTileViewInfoCore : TileViewInfoCore {  
        public MyTileViewInfoCore(ITileControl owner, TileView view)  
            : base(owner, view) {  

        }  

        protected override int SelectionWidth {  
            get {  
                return 5;  
            }  
        }  
    }  

Please test this approach and let me know if it helps.