Loaded question. Quantity have a quality of its own.

A small amount of donated money could land an employee in hot water with the employers/family/social circles (which we as a society don't want). A huge amount of money could outright buy an election - which is unhealthy.

The first enhances the marketplace of ideas. The second could drown any other ideas.

So money should be protected as a speech to prevent repression. Not sure if it is possible legally (even if we ignore the first amendment)