Con tendencia a quedarse calvo = With a tendency to go bald, meaning no hair.
La cara vista es un anuncio de Signal = may refer to a tooth paste, so it may be The seen face is a tooth paste advertising
De mi idea genial de echarte = From my brilliant idea to throw you out.
Olvidar quince mil encantos = To forget fifteen-thousand charms, like in nice and atractive traits.
Es mucha sensatez
Y no sé si seré sensato = Sensatez and sensato is related to sense, like having good sense, being smart.
*this refers to a word that can be read backwards with a different meaning like pat-tap not to be mistaken with a palindrome which is a word/phrase read the same forward and backwards ie racecar-racecar. So the singer means that this bifrontismo lacks a second meaning/significance