I think that we’re mixing apples and oranges here. Unless I’m mistaken, the original poster is looking for design- drawing software rather than proposal and project management software such as Bid Magic,SRS or D-Tools. While these programs may have drawing and design packages included, they are considerably more than a graphics package.
Visio is a capable tool, and with the appropriate templates and stencils it may be a very good fit for rack elevations, floor plans and wiring/equipment layouts. I’m not a Visio expert, but I dont know that it is capable of importing a CAD drawing however. So if floor plans are going to be a desired output, somebody is going to have to spend a bunch of time creating a floor plan.
An installer whom I really respect uses a product called Canvas. It imports Autocad drawings, creates layers (think one plan for audio components and wiring, one for video, a third for lighting etc). If the principal purpose is to create prints, this might be a product to investigate.
As with all software purchases, spending some time really exploring what the needs are and then investigating the capabilities of the candidates prior to purchase will prevent a lot of heart ache down the road.