I'd say there are definitely cases where remakes are justified. While the RE 2 and 3 remakes missed some opportunities, it offered people a fresh, modern way in which to experience those stories.

I'd also like to see more remakes of games that had good ideas, but were let down by the overall gameplay (looking at you, Silent Hill 4). Of course, the fact that these were generally less successful the first time round makes them a harder sell, which is a shame.