Alan, here you are:
The song is based on a true story about forgetting to pack a guitar , panicking on the plane half way to Memphis, and having the instrument shipped by train to Oriole Kentucky. On collection the instrument is badly damaged (electric junk). The shame presumably comes from being treated with indifference by the black shipping clerk, and possibly from being responsible for it ending up in that condition. The guitar belonged to Mick Ralphs although Ian Hunter sings the song in the first person. The incident is referenced in 'The Ballad of Mott the Hoople': "Buffin lost his childlike dreams, and Mick lost his guitar"
Ian Hunter is an old geezer, born pre-WW II, back then “spade” probably wasn’t the worst thing you could call a person of color in Ole Blighty. And certainly, the black GIs that began to populate the UK ahead of the Normandy invasion were surprised about the non-segregationist society they found. I’m sure he never meant it in a denigrating way, he loved what Black Americans brought to wartime England.
These days when he sings the song the “spade” is replaced with “dude”.
PS: I thought the same thing about Ace and Ariel. Being the Anglophiles they were, I’m sure Ace’s inspiration for his “stutter guitar playing” helped him win the audition with Paul and Gene. They had actually already settled for Bob Kulick when Ace stumbled in as the last guy they auditioned.