There was a window of oppertunity for a C64 with a Z80 for some more processing power

What screwed Commodore was downsizing essential development (R&D), nonexistant advertising, lack of straight line of model features. This seems to be caused by Gould allowing Ali (and other?) which lacked visions and were technological incomptent in to a controlling position.
Customers just won't spend money on the same crap in different packaging. It better have some cool features in the hardware.
Conclusion: Spend R&D, advertise, save money for hard times, have a vision!