The latest episode of EverFree Radio includes an interview with Cathy Weseluck, known to fans as the voice of Spike the dragon and the Mayor of Ponyville. The interview starts at around 30 minutes into the show and lasts over an hour.
Cathy discusses much throughout this episode including how she started out in voice acting and My Little Pony, the process of recording and episode and the voice of Rarity in an earlier My Little Pony show. When discussing voicing Spike she mentions how she changed voices as he aged in one episode, and does some example voices of that. She also discusses voice acting workshops she gives, as can be seen on her web site.