Not a bad idea, BUT....
Except for the 'test,' all this already exists in one form or another. You can buy Tim Marshall's chase guide for what? 8 bucks? Mike H. has a Storm Structure video for not a lot more. Etc, etc. Too expensive? OK, try Haby's Hints and a dozen other highly informative web sites. As always (it's a universal human condition!), the most inept people
- those who most need help - are always the last to ask for it.
As for the test itself, I think most of these people would sputter a few choice words at anyone suggesting they take such an exam. Again, only those who really don't need to take it would be remotely willing to do so.
I do agree that some informal level of 'credibility' would be very helpful for the NWS when they receive calls of a mean looking rainshaftnado that's about to erase a town. OTOH, we already have formal spotter training, and that's apparently not always working so well. I'm not sure what else can be done.