Well,
Some things simply don't exist in multi channel format. To try to "mix" a mono recording into multi channels is, IMNSHO, a tremendous waset of time. I've got some records that were "electronicaly enhanced for stereo" and the sound absoposilutely sucks.
And, some people will buy anything simply because it says SACD thinking they will get better sound, regardless if the original mono master is almost 50 years old. FWIW, I've heard some pretty smashing redbook CD's in my time.