This sounds like a production I saw some years ago. The Scarecrow, Tinman and Lion have intro's to their songs (and the crows, in the Scarecrow scene, participate). Yes, Glinda sang Optimistic Voices as they were headed to the gates. Merry Old Land of Oz had an extended intro at the start where the gateman guided them in and talked about stuff (LOL: my memory's shocking)
This is the production from the Royal Shakespeare Company, which was done in the 80s (and is very faithful to the original movie). There's another version, which I call "the bastard" which is very weird, and has a new song named Evening Star
It's not very pleasant at all
P.S.
I would love to see a production of Oz in which Pink Floyd's Dark Side of the Moon were the songs performed in the story. That would be hysterical: Dorothy singing Time, the Munchkins on Money, the Witch or the Wizard on Brain Damage.
Or I'd like to see a gothic, horror version of Oz or Alice in Wonderland
Who can explain it, who can tell you why?
Fools give you reasons, wise men never try
-South Pacific