I am constantly beset by my dwarves' unfulfilled needs to make stuff, because I obviously do not want low-skilled dwarves taking up workshops and work orders making low-quality junk. 0.50's labor system DOES slightly ameliorate this, but I don't think it's quite there--you're still having low-skill dwarves suck up valuable workshops and making crap.
So, I think guilds should hold classes for non-members, or classroom zones should exist that are linked to a guild. During a class, a guild member teaches any random dwarves that show up a bit about their skill, giving those dwarves experience in those skills. Dwarves, when on break/not doing a job, can choose to go to a class fitting their personality--for instance, a dwarf that likes rocks may visit a stoneworking class--or just because they wanna learn something new, such as a master engraver checking out a cooking class for fun,. The desire to go to a class may even be inspired by something that happened to the dwarf--for instance, our engracer may have wanted to learn cooking because they ate an incredible meal, while their own engraving inspired another dwarf to attend an engraving class. Classrooms can also have workshops attached where dwarves can make stuff in-class which also satisfies their "practicing a craft" need and gives them something personal they can keep with sentimental value.
Classrooms could also be used to very quickly train a set of dwarves in a skill much faster than just letting them do the job in question--dwarves could be assigned to a classroom and teacher, where they learn the skill without taking up your normal set of workshops (yes I know you could make a buncha new workshops somewhere else and assign them to the workshop, but I think this whole suggested setup is a lot more sensible and charming than just doing that. Plus, if you NEED a completely utilitarian justification, you wouldn't have to micromanage workshop assignments, burrows, and other related crap if you can simply assign a classroom and have dwarves come and go as they please or when you command them to). And, of course, children could be assigned to classes--perhaps even implementing an entire education system, where once your fort is large enough an entire public schooling system can be implemented. Nearby hillocks and other sites could also send their kids to your schools as visitors, which could help your civilization maintain a large pool of highly skilled workers (presumably this would also work hand-in-hand with other features that encourage caring about your civ besides trading caravans).