I find this all quite strange:
(1) Much of the music popularised by Gardel may be considered 'undanceable' but he is an absolute classic in the genre, and the idea that
a modern tango dancer would turn up their nose at the music or the lyrics of this song, which is a classic in Latin America (many latin americans outside of Argentina would also know this song) is quite frankly... well, I wouldn't like to say...
(2) I don't know what version of Adios Muchachos was played, but the Canaro version is IMO perfectly 'danceable' - yes, it is in a major key - sorry.
(3) It seems quite odd chosing what music you like or will dance to based on the lyrics - especially if it's tango music - which is usually about some flavour of unpleasant topic. So this one's about murder, and others are about lost love, unfaithful women, loss of home/country/friendship/ etc. If you want 'happy lyrics' either choose a different form of dance, listen to early Beatles, or else, try to 'unlearn your spanish'.