Thanks Yenthe. I lack the karma to comment on your reply so will do it here.

I'm seeking additional functionality - something that can be loaded on demand as either a full message log or as a clear indication of which customer documents have messages attached to them. Forcing Odoo users to hunt for message traffic that has been hidden in multiple silos is a recipe for frustration on both sides of the conversation.

Hi David,

This is basically how Odoo works by default. The idea is to have all the information for one subject on one spot. All the information about your sale order? On that sale order. All the information about your lead? On that lead. 
I think you should think about this from another perspective. Start from the customer form and then open the related record where you want information/history about. If the person behind the phone gets a call from customer X about sale order Y he or she will need to open and look at the sale order Y anyways. This means that if you open this contact his sale order that you find all info related to that sale order, nothing else.

If you should want every message that was said related to a customer in one view you could choose for custom development. As pretty much everything in Odoo is related you can create a new relational field that shows all e-mails related to a contact on the contact form. The question is if it is really that useful though. You'll get a huge load of messages and filtering/finding out the trace from one subject will become a bit annoying. Not to mention that if you have a contact with a lot of conversation(s) that the loadtime for the contact view will drop too.

I hope this insight helps you a bit.

Regards,

Yenthe