The Riddler is an awesome Batman villain that people need to know more about. Gorshin's Riddler was okay but not good enough, Jim Carrey's was horrible. We have yet to have a good Riddler on the big screen. Nolan made many villains darker, interesting, and more popular: Ra's al Ghul, Scarecrow, Joker, Two-Face, and Bane. Nolan has proven that he is a great director and he could definitely pull off a great Riddler.
Had Nolan redone the Riddler there would have been an expectation that the caricature raise to the expectation of the Joker from the second film. That is an impossible standard to meet! Sure the bar for the Riddler character was set pretty low with Jim Carrey's destructive take; but still with the work Nolan put into the remaking of the Joke there is no way that anyone would be able to fit the bill.