Dick, having not attended the conference, but having recently attended design classes at Pingree Park and having the vantage point of a novice designer, I would have to say that engineering classes are not beyond the scope of a conference with some qualifications added.
I may be going out on a limb here, but I have to agree with Mark, that most but not all attendees would have some basic interest in engineering. Their level of understanding would be greatly affected by their prior education and experiences. Some of the attendees may have wanted nothing more than a system to use or compare to their own way of doing things. Others may have wanted to get down to the nitty gritty of why things are done a certain way and others may have only wanted some "rules-of-thumb" by which to assist them in everyday business.
In fact, one of my chief complaints about the class that I attended in Colorado was that some of the material was highly technical in nature and with no way to corrolate that information to the real world, I believe that I missed out on some real valuable information. Several students were just fine with the presentation, but I later found out that those students were all degreed engineers. Those of us who weren't engineers were lost.
My intent here is to be constructive, so I would volunteer that any seminar should be directed at a target audience that is either defined by the instructor or by the audience. If the instructor sets the agenda, then it is a simple process for the instructor to limit attendence to only those who are qualified to attend. If the audience sets the agenda, then the instructor has the more difficult task of adjusting his presentation for the benefit of those attending. Since more than likely, the audience will set the agenda, I think that I would take a limited subject, such as beam sizing, and focus on developing an industry wide "system" for beam sizing and keep the "techo talk" to a minimum.
As a side note, there seems to be a general trend among the many "non-engineer" designers that I have met with of the appearance that many don't understand design, or they are in search of a system to use or they simply can't communicate what they do because they rely too heavily on software to do the job for them. Of course, of those designers that were educated and decreed engineers, that trend was noticibly absent, although some were still unable to communicate.
I'm sure that my thoughts will elicit some hard line comments. Please accept my advance apologies for any feelings that I unintentionally harm.