Prince never used orchestra on stage
he never tried his "Concert or group and Orchestra"
Deep Purple made one of the best albums in that field,
while Metallica failed big time.
Superbowl performance had marching band and it sounded interesting.

Yes Prince used orchestrations of C.Fisher but he never made his own attempts
Some of his songs can sound great performed like that,it can give songs the bigger feel.
imagine Prince and his band with large orchestra playing this setlist live:
17 Days
Raspberry Barret
She's Always in my Hair
When U Where Mine
Venus de Milo
I Could Never take the Place of your man
Old Friends for Sale
Life Can be so Nice
Moonbeam Levels
1999
Diamonds and Pearls
Lets Go Crazy
Purple Rain

(this are not my favorite songs but the setlist that could sound good with large orchestra )

or imagine even further Prince doing music scores for movies and remading his songs like Venus de Milo

Purple and Gold

Flute always sounds nice with Prince's music. I think an orchestra would be grand. Somewhere Here On Earth would be great too.
[Edited 1/22/10 14:26pm]

currently listening to Madhouse 8... what would be cool if P could incorporate some electronic elements to the orchestration like on some of the madhouse cuts. HMMM, HMMM, HMMM... ya dig

ive always wanted my school band to play 3 chains o' gold..that would be amazing or old friends for sale in my jazz or pep band.. ))