I think it would be useful having a group of pictures, either online or in a publication, that demonstrate certain specific aspects of a note, things like embossing and cup marks and rippling and "thumbing". But that is something completely different from a visual grading guide that would attempt to attach a specific grade to a specific note.
A paper money grading guide would not be helpful to the average person, IMO, for a slew of reasons. For one, it would create a sort of dependency, thereby removing the need to learn. Such information could also be used to create and heighten grading disputes between sellers and buyers since buyers are always looking for excuses to downgrade a note they are thinking about buying. In other words, it could be abused and create lots of headaches when people start counting folds and creases and argue over arbitrary things, like saying a VF can't have more than three major folds, so a note that has three vertical folds and one horizontal fold or a corner fold can't be more than Fine. It's bad enough that "experts" are giving consumers what amounts to standardized subjectivity in the form of third party grading (i.e., companies like BCS, PCGS, PMG, etc). But grading is still subjective, and giving the consumer something like a standardized visual grading guide would amount to trying to take the subjectivity out of something that can't be quantified or measured.
The Charlton catalogue tried removing some of the subjectivity out of grading in its verbal grading descriptions a few years ago. I think it was partially a failure at best. The demerit point system tried to quantify differences between the three Uncirculated grades, but it created new problems in the process. For example, a Choice Unc note can only have one demerit point, so a perfectly centred note with one crease is Choice Unc-63, but what about a poorly-centred note with one crease? That's two demerit points and therefore such a note would only be Unc-60. Cup marks are original features of Journey series notes, but they are considered a demerit such that only notes that lack them could ever be considered Gem Uncirculated. Ripples used to be negative feature too, but now the guide tells us 1954 series notes should have them, so ripples have been promoted to a requirement instead of a detriment. Will the same thing happen to cup marks in a few years? Will people start saying Journey notes need cup marks to prove that they are original and uncirculated, otherwise a flat note without a cup mark could be pressed?
The bottom line is there is no magic bullet to learning grading, just as there is no magic bullet for weight loss. Weight loss takes time, effort, and dedication (unless you want to cut off a leg, lol). Learning to grade is no different. It takes effort to understand how notes change appearance as they circulate and that not all notes change in the same way.
I would like to add that comparative grading is a very dangerous practice. This is where aesthetics really comes into play and can fool a person. Sellers use this trick all the time. You have two notes of the same series, and they are very close in overall grade. The slightly better note can sometimes look much brighter and fresher when it is next to a note that is dirty and impaired. The seller can generate a much better sale price for the slightly better note using this juxtaposition technique as opposed to trying to sell the note on its own merit. This technique really prays on the average buyer's aversion to "problems" like small edge tears, pinholes and graffiti, and some people will be caught paying way too much for a problem-free note.
I understand the need of the average collector to have assurances that the notes they are buying are exactly what they are expecting. There are lots of people trying to sell sub-standard material like it is much better than it really is. However, I would like to point out that Canadian notes are an absolute bargain compared to notes of other countries. The only reason Canadian notes remain so cheap is that there are hardly any serious Canadian collectors, and consequently, there is a glut of just about everything on the market, and because of that, the average buyer is a whiny skinflint. Most of the people buying notes these days are interested only in investment potential, not in the hobby aspect, and that's ironic because Canadian paper money is a really lousy investment tool.