It might be interesting if a lot of the current workshops were designated from furniture, rather than placed as a simple 3x3 object. And the effectiveness/functionality of the workshop would be dependent upon the furniture in the workshop. It could perhaps even be the case that no workshop is of a specific type, but is just a generic workshop, and the jobs that can be done in it are determined by the pieces of furniture in it. Additionally, more than one job could be performed at a single time within it. (Getting complicated, but still, idle fancy and all...)
For example, a room could have some form of a stove, molds, and an anvil (and anything else I'm forgetting that would be appropriate), and could work as a smelter/forge. Smelting and forging could be going on simultaneously in that same room. Two anvils in the room would allow two forging jobs to occur simultaneously.
Another thought bassed on this is that certain jobs could be multi-stepped: The dwarf would need to use different pieces of furniture in a workshop throughout the process of making the final product, and thus the layout of the workshop could at least slightly affect the efficiency of the workshop. Example: A kitchen might have a stove/pot, an oven, a table, and a cutting board (trying to be detailed to emphasize the multi-step process). The cook, when making a fancy meal, might need to first use the stove/pot to heat some water. Then run over to the cutting board to cut stuff up. Run back to the pot to dump stuff in. Run to the table to mix/knead some dough. Run that over to the oven to start baking it. Run over to the pot to stir. Run back to the oven to get the baked bread. Drop that off at the table. Grab the pot from the stove, and again drop that off at the table where the two items are combined. Poof: meal. If the kitchen is a large kitchen (intended for simultaneous cooks, perhaps), and the table is in a far corner, it might take a wee bit more time to complete. Also with the kitchen example, the kitchen might include three ovens, but only one stove/pot. If all you are doing is baking stuff, you can easily have three cooks running at near maximum capacity, but anything requiring a pot is going to to encounter a bottleneck. But this flexibility allows you to customize workshops according to your typical usage scenarios.
One final thought: Moody dwarves might need multiple types of furniture, since they often work with vastly different types of material. They might even need to run from workshop to workshop during the course of their crafting. Perhaps instead of claiming a whole workshop, they'd merely be claiming pieces of furniture, and only as they need them.