Definitely not "plenty of time" unless the OP's flight from DCA is early. Likely the flight from DCA will come into D (maybe OP will get lucky and the flight will come into E gates). If it's lower D even with the Skytrain the schlep to E, particularly if it's the satellite gates. Remember even if the flight from DCA pulls up to the gate right on schedule it can be another 5 minutes before the OP is actually exiting the a/c (jet bridge operations at MIA are very slow). With a 52 minute connection the "minutes" matter.