Elucubrando comes from the verb 'elucubrar', which means to speculate, ponder, or elaborate on something, often late into the night or with great effort. It's a more formal and less common word than simply saying someone is 'thinking'.
In the song, the line "Por eso elucubrando en este asunto" ("That's why speculating on this matter") shows the narrator deep in thought, turning an idea over and over in his mind before reaching a conclusion.
Carlos Vives built this song around one simple piece of advice: stop waiting and start living. He opens by noticing what's fading, singing "Ya no se escucha a los viejos de la manada" ["You no longer hear the old ones from the pack"], and turns that observation into a reason to grab the moment with someone instead of dwelling on what's gone.
The title comes straight from the hook, "Yo sigo los consejos del difunto" ["I follow the advice of the deceased"], and Vives keeps that advice light rather than solemn. He tells a quick, funny story about bad luck: "Yo pesqué un arenque" ["I caught a herring"], only to hand it straight to the cat before he could keep it for himself. Right after that joke comes the line that matters more to him: no money, but a good woman is worth more than any fortune. By the chorus he's inviting everyone to Cumbiana, his own festival, to dance the cumbia while there's still time.