This is a great question and really comes down to sales approach and system philosophy.
Are you selling a system or parts?
If you are selling parts, then images next to line items in proposals I agree have a positive impact.
If you are offering the client an experience by way of telling a story and selling a system, then small thumbnails next to pages of line items in a proposal sends the wrong message by foucsing the client on the commodities of your offering...the parts.
Creating a project in text to get a concise proposal focused on systems by leveraging packages can be accompanied by a simple line diagram or room summary that uses images not even loaded into the D-Tools databse (saving you time managing images inside your database).
Create an illustration of your system in a larger format such as 11 x 17 or even 24 x 36 using visio along side D-Tools or the Line Diagram page in a D-Tools Visio Drawing.
You could even create a collection of system illustrations in Visio using images not related to D-Tools data that represent hundreds of products that you use (sell) in your systems.
Either way, a small collection of images that represent each Category and Type of core product that the client will see and touch can be kept outside D-Tools and quickly copied, resized, replicated, duplicated, without relationship to D-Tools data, making the develoment of such high impact visual illustraion of the system.
The advantage of not having images tied to data is that you can copy and paste tham into projects without having a specific product associated with the image.
Data tied to shapes for plan, elevation, and schematics is crucial for creating engineered drawings, but for these picture or illustraions, we have found it binds you up rather than looses you productivity.
Attached for your review is a proposal and a set of systems illustrations.
The illustrations were created in a D-Tools Visio Drawing with a collection of images stored in a folder by CATEGORY and TYPE that match our D-Tools product database for easy insertion to the drawing. Later, additional drawing were created in the same visio project file using D-Tools shape data to dicument the plan. elevation, and schematics.
Another approach can be seen in the sample project on our website.
Process Dealer Services Group - Serving Digital Home Technology Integrators, Electrical Contractors, Architects, and Homeowners