James, please do write that letter. I agree that we shouldn't discourage use of a good, strong harness bar. I also agree with you Pat, in that parts can be designed to be reasonably strong, but not provide structural enhancement. However, why should we drive folks to design and fabricate parts (especially in stock class), when there is a selection of off-the-shelf parts available?
IMHO, in the majority of cars the bar provides a negligible amount of stiffening, but the rule (13.2.I) doesn't say negligible, it just says It may serve no other
purpose (e.g., structural enhancement). That, to me, is saying no amount of stiffening is allowed, which is why I'm not currently using a harness bar. 
-Steve