Junk you bring up some good points and the ADA laws have been interpreted, reinterpreted and misinterpreted so many times that unfortunately nobody has a final answer until you end up in court.
Generally there are a lot of easy accomodations that should be complied with right off the bat. Parking spaces, entry doors, aisle widths and bathrooms. When doing new construction, if the building is in the planning stages these things can be accomodated easily and with little to no added expense.
What gets tricky is when you remodel a building, at that point you have to bring everything up to the ADA standards.
There are also issues with PUBLIC/CUSTOMERS versus EMPLOYEES. The standards are different and that is considered reasonable.
You typically have to be far more accomodating to the public than you do to your own employees. For example, I have narrow aisles in my warehouse picking areas. No way to get a wheelchair down those aisle. But that is acceptable because of several reasons. First, the public is not allowed in those aisles. Second, the shelving is arranged such that you must be standing to perform the work. There is no way to accomodate a wheelchair bound individual and still reasonably do the job. That specific does not then allow me to ignore all wheelchair access. It just permits me to not have wheelchair access in that specific area, but my office areas need to allow for wheelchair use.
In Dave's case, and I don't know all the specifics, but generally it is reasonable to accomodate people by having a viewing area that is not on the upper level. Think of a bank, they often have a service counter for people who use wheel chairs, it is rarely staffed but if someone shows up in a wheelchair the tellers will accomodate that individual and then return to their normal station, so it does not require another employee, the employee just shifts position temporarily. Dave can provide a separate area and it does not even have to be left empty 100% of the time, he just needs to make it reasonably accessable when it is needed.