I think it partially depends on what's in the tool. Netzoom has a team of people that create the stencils. The turn around time is usually couple of days which is EXCELLENT. This is not just for the visuals but ALL of the connection points as well. The data portion is similar to ConnectCad where you add in weight, power manually.
The last time I used them I believe they charged around $700 per year which I felt was high relative, to what you got as it relates to Vectorworks/ACad/Bricscad etc. To be honest, for the cost of Spotlight + ConnectCad and the fact that most of the functionality is already available, I feel it should be included already (w/caveats). Your additional $250-300 feels reasonable. I would consider paying more for the device to have full information included: dimensions, weight, power, btu's, but I don't know if it's worth the extra effort on VW's part especially since some manufacturers don't readily provide this info.
Would the tool allow the importation of cad blocks directly from manufacturers (this we can already do it's just not a part of Device Builder)? Would it include an editor to allow the complete creation of the block if not available from the manufacturer (This we can sort of do via Panel Builder but the panels would need to be attached to the device)? Since most of the tool is already in Vectorworks, they'd need to make the business case for modifying the software design so Device Builder and Panel Builder are more integrated and make the business for creating accurate symbols in house and including them in the library.
My take is it should be VW provided and community based. If VW provided, each device needs to be as close to perfect as possible. If community based what becomes available should be as-is. This means if I create something that is incomplete, VW has NO responsibility to fix it and we use at our own risk. VW blocks should be labeled as such so we know they are complete and Community blocks should be labeled as such and each creator should state the level of completion, notating what is missing. From there it would be excellent if there were a means for VW and/or the community to update the device and the level of completion. VW would only need to verify that it is correct before receiving their stamp of approval to it's level of accuracy.