Great, thanks; I see what you are wanting now...
Let me clarify how this will be addressed in the future, so there are no surprises. Some of this will reveal our 1.0 roadmap, which I’m trying to find time to publish formally (sigh).
First, in 1.0, Documents (which I will refer to as Resources, since they represent any web resource accessible by a URI) will be represented by classes and can represent a lot of different things, from links, to typical pages, to AJAX request handlers, to SOAP handlers. Document Types as they are now, will become the Resource classes and will define all the data to be persisted for and the behavior of that class of Resource, overriding only what it needs to in order to accomplish it’s extended purpose.
Second, in 1.0, manager pages can be standard PHP pages that can access the MODx object (aka controller) just like the standard front-end pages do, or however they decide to. This means they can take advantage of the parser if they want to (or not), use individual snippets or other Elements (in 1.0, all currently named MODx Resources, such as snippets, chunks, TV’s, plugins, and modules) directly; in other words, a PHP page can have all the advantages of a page managed in the MODx database as a Resource.
Finally, the user systems and permissions will be integrated in 1.0. No more web users vs. manager users. A user is a user is a user, and they have permissions that apply at various scopes in the site. Thus, in 1.0, you could decide to implement a manager interface along with the standalone manager php pages, or create an interface just like you would for the front end, from your existing manager pages, in a secure context of the site (i.e. you might divide a site into a public site and a private, secure extranet site, which would be different site "contexts" in 1.0, but more on that soon).
This means, the manager will be a completely customizable interface at your disposal, modules essentially become just another way of attaching a content element (any kind of content) to a web resource, and you could accomplish all of this by simply creating a MODx page as usual; and you probably wouldn’t even need a custom Resource class to handle it, though nothing would stop you from implementing such.
I hope that vision of things to come in MODx helps you in your decisions when choosing to hack the current system in this regard.