It should give you a realistic starting point for planning your security response to the risks you've identified. Something that is safe today may later be discovered to be unsafe. Your risk assessment and security procedures must be flexible enough to adapt to new information about the state of security, or you may find yourself comfortably ignoring new problems that may apply to you. For your list of risks and damage assessments, attach a set of likelihood factors to them. If you've got a lot of high likelihood risks that carry high damage estimates, then you've really got cause for concern.
Defensive tools are available for practically every computer security problem.
Your challenge, as someone implementing security, is to make sure that the right tools are employed where they are going to do you the most good. Obviously, the first places you should begin to protect are the most likely points of attack. Consider storing some of the Web pages on read-only media. Large organizations should centralize dial-up behind a controlled and auditable modem pool. For systems that are vulnerable to viruses, install virus scanning software as a matter of policy.