You can reference the NotesXspViewEntry by using the collection name variable and getColumnValue(). So, in your example I'm guessing you could use rowData.getColumnValue("lcname") and this will definitely be faster than getting the document and then the field name from that. But you are only talking fractions of a second so unless you are processing lots of documents per page then it's not something to worry about too much.

As far as my understanding of the difference between the two objects, it is just that. The NotesViewEntry object has a different set of methods and properties. As far as I know there is no way of casting the objects from one to the other in either direction.