Groundhog Day was superior, so maybe he needs Murray to excel.
Akroyd is a creative nuclear bomb, but he actually believes some of that stuff. That force has to be managed. It was managed originally on the first film by limitations of FX, now I would be worried he would go nuts.
You may have a point there - Ackroyd + the limitless possibilities of CGI, I'll bet that combination may come up with something that could make even Lucas's eyes bleed.