The main purpose of a dashboard is to give a summarized and an 'overall' view of the system/ application and it's data. A good dashboard is one that gives all the information to the user, in a nutshell. He should be able to get an overview from the dashboard itself, and if he wants to view more on any topic, he should navigate to inner pages.
Having said all this, the dashboard should be highly customizable. The user should have the option of choosing what to see in his dashboard and what need not be shown. It is not advisable to change the theme of your dashboard, with each type of user. The theme is the soul of your website. If you change the dashboard theme based on various users, there will be a lot of work involved, as well as there will be a higher chance of inconsistency.
In my opinion, you should provide a standard dashboard for all users, with variations of contents, based on the user. A customer need not now the details of other customers, but a broker needs to know the details of all his customers. So the dashboard should be customized accordingly, wherein the customer only has the options to view data that is relevant to him and the broker is given all options of data, which he needs.
You can keep a default element as a content for the dashboard, and provide options for the user to change it, modify it and customize it.
Suppose I am a stockbroker. The first thing I want to see in my dashboard are details of the market values for the day. Also, I would like to see a summary of how many customers are going to gain a profit and who all are going to lose money, and by what margin. Now, if I were a customer, I would only want to see if my numbers are good, and the status of my stockbroker. I only want to see the status of the shares I have invested in, atleast only that in my dashboard.
So, the best form to retain consistency is to maintain a single template or a theme, and customize the contents based on the type of user who has logged in.
Note: You dashboard elements should never be fixed. It should be flexible, modifiable and interchangeable.