The 128 was cool, but 85 was totally the wrong time for it. In 85 cp/m was dead, msdos killed it mac buried it and amiga and atari pissed on the grave. In 82 or maybe even 83 a dual boot capable c64 with cp/m would have definitely turned heads. It probably wouldnt have saved cp/m, not by itself but it would have sold.
I thought the plus4 was an interesting design but it was poorly implemented. Better, more up to date software like the plus4 had but on a cart would have been better. The video chip had some good features with lots of colors but it didnt have sprites or a sid chip.