My wife also says "All his voices sound the same!"
Of course, she doesn't have the keen ear we do. I've broken down Wurster's vocal range into the following categories, with some examples of each:
Regular Voice, High-Pitched: Darren, Drunk Driver, Caesar
Regular Voice, Low-Pitched: Bulk of the characters
Calm Scratchy: Corey Harris, Reggie Monroe
Angry Scratchy: Mike Sajak, HRR, Andy in Lake Newbridge
Old Coot Voice: Gorch, Cardiff Giant
Authoritative: The Music Scholar, Roger Scharpling -- except for the birthday call from a couple years ago. For some reason (laziness? cocaine?), Roger's voice was RV-LP during that one.
Funny Voice: Zachary Brimstead, PBR, Bryce, Timmy Von Trimble
Funny Voice One-Off: Todd (Audio Guru Disciple)
Funny Voice Foreign: Bishop Pablo Fontana, Rodrigo, Corey Harris's Nurse
Funny Voice Impression: Marky Ramone, Gene Simmons