Would it make sense to use an adaptation of the Aesthetic Quality rules for Artists in A&A to allow items to be studied for XP in one or more of those areas, whether just for Verditius or for all magi? Could it be done in the same season as one investigates the enchantments on the item? Would it make the Verditius Contest more attractive to compete in (as the items chosen as prizes could also be good study sources)?
Off the bat, studying an object created with a Craft ability is useful as a study source for that ability, according to A&A, so this is doable. It uses Aesthetic Quality/2 as Source Quality. It is aseasonal activity, and although A&A does not specifiy I would say it is useful only once per student. Although larger items should be useful for several seasons of study, a cathedral should perhaps be useful as study source for longer than a jeweled ring.
As for studying it for Magic Theory? This doesn't sit right with me, the Aesthetic Quality isn't IMHO tied into the magic to warrant this.
As for Philosophiae? I'm kind of wavering on this. On one hand is seems as unfit as Magic Theory above. On the other the Verditius did use runes, metaphysical relationships etc. and these are visible like the handiwork of the craft used. I might be tempted to go with this.
But can a single device be studied for both Craft and Philosophiae? Well, if I open the door for Philisophae I may also be inclined to allow one season of study for each of the two.
However, I would not let thisstudy be combined with a season of Investigating the Enchantment. Both of these are seasonal abilities in their own right.
As Christian Anderson says, it can already be studied for the type of craft used to make it, and I would support Aesthetic Quality being a criteria in the Contest.
I do not support using it to study anything else because there is an entire economy based upon MT tracti that this would upset dramatically in that this would create plentiful SQ10+ sources that would obviate the need tp ever write MT Tracti. Philosophiae has plenty of good SQ mundane sources, so no need to add additional there, although if you did it would not change the game balance like MT would.
C&G does IIRC mention 'craft manuals' but since the bulk of Craft ability using persons in ME are likely to be both non-magi as well as illiterate I don't envision these being very widespread. As I see it Crafts are improved through Training by a master, Practice as well as Exposure while working.
Maybe Verditii (or more likely their Forge companions) would bother spending time to write books on Crafts. Or maybe they would study devices instead? Sure, Quality for this is ½ Aesthetic Quality, but this can be quite high for a true master. And perhaps Verditii spend their characteristic points on Dex rather than Com, so this may easily be higher than Com+6 for a book they wrote.
But access to other Verditii's masterworks is needed! Would a magus buy such a device in order to study it? Would he even need it for an entire season? Looking at A&A the text says about studying a Performance that merely watching the show is not enough, it needs to be re-created, reherarsed and otherwise analyzed. So for a device, how much time would you need to physically observe the object? The remainder of the season could be to ponder over sketches, notes etc. Magic could be used to see greater detail - IIRC HoH:Soc-Jerbiton chapter has an InIm spell to see details - or use magic to enhance or refresh the memories of seeing the device, or even to create an image to see, touch etc. the device.
These difficult questions need answers before the itemn can be studied, that should spark a good discussion in the Troupe.
The real issue is that making art has different rules and time requirements than making invested items, and something that might only take a season to enchant might take two or three seasons (or years, or decades, even) to actually make using the art rules. I think many items would be deliberately made "non-artistic" to avoid this time conflict. Only the smallest, easiest items would ever be made using the A&A rules, limiting their use for study. Talismans might be an exception to this rule because they are typically enchanted over several seasons, so the time to make it "pretty" would not actually cost additional seasons.
The Verditus Outer Mystery does let the magi perform impossible feats of craftsmanship - if a Verditus can invest an item in a single season, they can make it in a single season. It explicitly says "Impossible by mundane means", so they can make art impossibly fast (at the cost of Vis) if they want. It's theoretically possible to exploit this to do stuff like making a Cathedral in one season, but it's a LOT of vis and it would be cheaper to do it with a ritual spell.
For the record, we already play that a Verditus can use purchased art as Source Quality for their Craft skills. It's not a big deal, as art is likely to be much more expensive than hiring literate Craftsmen to write books for you to read.
I don't agree with your interpretation of "impossible by mundane means". I think Verditii can produce some specimens of craft and arts that are 'technically' impossible by mundane means. I don't read into it at all that they could build a cathedral in a single season, something dozens of workers spend decades on.
The example goiven in the core book mentions setting a gem in a wooden lattice with no visible joints. A non-Verditius magus could do this with a little MuHe. No mention of time reductions.
I'll give a lot of room for impossible, I'll admit. But they mystery does let a Verditus shape the raw materials into an appropriate item in the investment of an item, and investment takes a season. It doesn't put reasonable limits on it (though the base game sort of assumes that something the size of a room is the biggest enchantment you can do).
You'd need an incredibly huge lab to do it (which may end up being impossible in and of itself), you'd have to assemble all the raw materials at the site, and if you were just making a cathedral (rather than throwing additional enchantments into it), it's more expensive on vis than just using a 'Create Cathedral' spell (and may well take more time than inventing the spell). And if you don't have a lot of Craft: Mason, the Aesthetic Quality of it will stink.