Old ideas always pop up. 'Remember that magician from three years back?' That's not a problem, that's normal. What is a problem: letting them dominate the session.
Three things help:
One: write the old ideas everyone already knows at the top of the board, and cross them out. They can't come back as a proposal.
Two: change the perspective halfway through. 'Suppose we had double the budget: what wouldn't we buy then, but actually make?'
Three: bring in someone from outside who doesn't know the company. Honest, naive questions ('why should that even be the case?') break patterns that have become invisible inside.