I've had this happen before too.   Spray it again with the varnish (ensuring it's not too humid out).    Similar to the Lahmian medium it clears a lot of it up.   not 100%, but left me with a few touch ups vs. completely repainting.  

I do like the singing, but my feeling is that it muddies the speaking voice and causes some of it to be more difficult to hear correctly.    I can get behind the idea of the samples at the end of a chapter/act, depending on the length of chapters. Personally, I wouldn't want it to be too often but would be good if used at the end of an act or after a major plot point/milestone had been reached. Give it a bit more gravitas.   

Cheers, I'll give that a go and see how it goes!