BEagle - this sounds like a case of "he who doth protest too much" -one test every six years!! Hardly onerous. When I became an instructor I did four tests in the first three years in order to become a MEI, then to upgrade to QFI on singles and then to upgrade to QFI on ME. I learnt an enormous amount every time I did a test and I consider that it is only in the one to one environment in the air that any unusual habits or misconceived methods can be straightened out. If someone does not want to take a test I am curious as to whether they are doubtful of their own ability. In the interests of imrpoving standardisation regular testing is surely desirable.
By all means have a seminar - it is a useful forum for conveying large amounts of material to a large number of people. I would be in favour of both being compulsory, although I believe that the schools should pay for the attendance by their instructors. I also think that three years is far too long between tests. Effectively a new instructor need never be checked again by test, which is as unsatisfactory as the PPL who never ever flew again with an instructor; at least they now have to do the dual training flight on a biennial basis.
By the way BEagle it may have cost a little less to attend the seminar but did you factor in the two days of lost revenue (as opposed to half a day if you do the test) or are you in the fortunate position, not enjoyed by the majority of instructors, of having a salary?