It is obligatory! I thought the 'Wally' phenomena was a Midlands thing. Are you a fellow Midlander?
Maybe it was more widespread... What was all that about anyway?! I remember, as an impressionable teenager, being told that Wally was a guitarist in some band and he was fatally electrocuted on stage. The shout of 'Wally' at gigs was a tribute to him... This was way before the phrase, "You total Wally" became prevalent...
Dyed in the wool Mancunian!
Before band appeared on stage Wally' was called out at most gigs at the Manchester Apollo (my experience being from late 70s onwards). Often the calling would strike up when roadies were making last minute preparations on stage etc, happy days.