I like it, even though I'm not much for crafting... yet. The idea of simply buffing a stat would automatically make a crafter 2-5x better at their job very unrealistic. As was stated previously any craft takes time, and only time should be the factor to improving it. Working and shaping metal for whichever outcome was a laborous effort and one that didn't happen overnight (not to say we need to force realistic timeframes) ones trade is developed by not only understanding the process, but also through conditioning of repetition of the physical work, simply making oneself stronger or sudden synapses firing to make them smarter while seemingly the numbers would work.
In theory a weakling becomes a hulk while doing the menial job they have always done.. progress would not be made, I would think much more in the effort of setback would take place as many things they had learned to do within the confines of their former physical self will have been unbalanced by the sudden surge in strength they are not accustomed to, breaking material.. bending a hammer.. twisting the metal to much.. etcetera. Though.. these are obviously realism factors not simple game mechanics and stat crunching.
Now on the side of arguing for the stat buffing. I would say that it could work as well, just..that any benefits of experience would be removed/nullified as the person is augmenting themselves to complete something in a hurried fashion. It isn't the state of mind or body they are attuned with and therefore any gains made would fade or have taken a corrupted process. For example increasing ones wisdom or intelligence would give great insights or realization of the process, but fade once the spell wore off.. becoming once again the mundane person they were.. forgetting some of the insightful clues or nuisances they uncovered while working. Notes the had written would more then likely be scrawled in a jargon or chicken scratch that made sense when enlightened.. but be confusing and read like little more than a madmans fervorous documentary utilizing the entire piece of parchment in no particular ordered fashion as they make best use to waste not the time or space available. At least to the duller senses.
Much like someone who has taken a drug that made things click on a substantial level.. yet seem deluded and uncertain once the high has worn off. I've experienced this on some occassions in my younger years while on a mushroom high or the few times I experimented with LSD. Interesting moments of levity, insightful conversations and theories sprung out of such moments, though once sober and recollection of the nights journey left the pieces distorted and without a linear path. I'll conclude any mental stat buffing to be much in the same once it has worn off.