Even though it's unfortunate that we don't get decent extras on the DVDs, I'd point out that many times a cast member's commentary often fails to live to expectations, especially if the cast member is doing it alone and he/she is seeing the episode for the first time in many years. Case in point was how on a recent DVD release of the 60s sitcom "That Girl" episode "commentaries" by Marlo Thomas consisted largely of dead stretches of silence punctuated by a few chuckles of her reacting to events on screen with no further comment!
Now if Peter were doing a commentary with Mark D. helping him along in the rough spots (or any other fan who knows the episodes inside out) *that* would be worth hearing! But I have to wonder if by himself, Peter would live up to expectations.
One person I know would have done a great job on a commentary based on what he's done elsewhere is Robert Culp, who in an "I Spy" commentary even referenced one of his Columbo experiences (the improvised bit in "Death Lends A Hand" when he wipes the food off Columbo's necktie).