Without an identify, these items are too hard to determine, but Gil-Gandel knows enough that the old Dunedain Blade is not going to be as effective as one from Gondolin. It won't do double damage but is likely just makes it easier to hit and damage.
Rorimac realizes reading from the Ranger book with the help of Belethil again, that he will be able to learn a wide variety of spells that he has seen Mages and Druids use.