If someone said "hey I've done a couple books on tactics and I don't drop my knight on move 10 anymore, what should I do now", then i'd recommend an endgame book. The Pandolfini book is a good one, despite its errors. It covers basically everything that Silman does, but it's in workbook form.
HOWEVER, any good tactics book will cover/teach endgame basics as well IMO. Bain's tactics book contains some basic endgame themes in it, although it's mostly a middle game tactics workbook. Ivaschenko's tactics books cover technical endgames as well.
I agree with Shivsky. Chess should be learned backwards. The FIRST thing to teach someone whould be how to checkmate with a queen.