There is no right way to measure the impact of good communication and poor communication. However, it can be done. More importantly, good communications is essential for a company to grow. In light of this, let me suggest a few ways in which it might be possible to measure the impact of good communications.
All businesses should have a time of internal evaluations. So, during this time, you can ask people has there been good or bad communications. This feedback will be essential. With this feedback you can ask what impact has this had. You can also ask another question about weaknesses. If people say that communications is the weakness, then you know that it is adversely effecting the business.
You can also look at positve areas of growth and seek to determine why this sector is doing well. Part of the reason may be due to the great communications between the team members.
By doing internal evaluations, you should be able to know how well people are communicating and what effect this is having on the company.