Should Isa & The Filthy Tounges cover Goodbye Mr Mackenzie & Angelfish material?

Answer 1

I don't know who any of those performers are but my answer is yes. A good song is any song that has meaning to you, so if the members of the group like the songs of others, the group should consider performing them.

Some of the all-time great songwriters and performers have played the songs of others, including the Beatles, Rolling Stones, Bob Dylan and Bruce Springsteen.

So yes, a performer should always consider performing songs that s/he enjoys. That is how performers grow.