\DeclareUnicodeCharacter{00A0}{\ } FWIW, A0 is supposed to be a no-break space. That's \tie, not "\ ".
\DeclareUnicodeCharacter{03C0}{$\pi$} Can you please send me your list of added characters? I know well that many math characters are missing, and I'd like to add them. (Except, better to use \ensuremath\pi than $\pi$, in case the character is used inside @math.) I'd rather not have to include texinfo.tex in my package. Is it a GNU package? Best, Karl