Should I dispose XtraGrid elements if it was created in code (f.ex.: If I add EmptySpaceItem in LayoutView)? Or GC collects it?
Basiclly, No. The GC does that for you.
Because the GridControl is itself a control, it is stored in the forms Controls collection. It will be disposed then the form is disposed.
XtraGrid is itself responsible for disposing any objects that lives in the Grid.
If you were to add a custom event/property to the XtraGrid, when you are resonsible for cleanling up when disposed is called. But it is not the case in your senario.