I don't dislike Santiago, but didn't find it overwhelming intriguing. It's clean and safe and a bit staid, so not as interesting as other South American locales. That said, I think Valparaiso has loads of interest and character, even if it a bit rough around the edges. I do like the views of the Andes from Santiago. If you can swing it, probably 1-2 days max in SCL/Valparaiso - depending on how your flight timings work.