It should be possible to choose whether a dwarf should rush out crappy crafts or take longer and increase quality. However, I don't think you should guarantee a certain quality of work by taking longer. If you give a toddler a crayon and all the time in the world, he still can't draw the Mona Lisa.
There should be some kind of easily-changed value (maybe a slider in the workshop menu) that ranges from 0 to 4, where 0 is favoring speed and 4 is favoring quality. Maybe some skills could even have subskills that determine speed and quality.
For example, the speed formula could be something like this:
speed in steps=(
?)*(N)*(4-(speed/quality setting)), N=speed/quality number
The quality formula could be whatever it is now but with an added thing where the speed/quality number is added to the skill level before calculations are made.
For the experience, the formulas could be (speed subskill)=2T*(4-N)/4 and (quality subskill)=2T*N/4 where T=total exp earned.
The main skill level would be calculated by adding the two subskill levels and dividing by two. This means that you could have a dwarf whose speed becomes limited only by how fast his muscles can react to an impulse but he will continue making crap until you command him to slow down a little and work on his quality. It also means that a legendary craftsdwarf would have to have legendary speed AND quality subskills.
The formula should be balanced so that the net value multiplier is slightly higher if you pick speed, because modern industry has reflected this. Also, it would balance the fact that the reduction in hauling and resource use would make quality seem like the best option.
Possible uses for this:
-You want high-end furniture for a noble built quicker
-You need to build cheap bedrooms for a huge wave of immigrants on the double
-You are too lazy to select 200 crafts for trade and would like to have fewer but better crafts
-You want to spam low-quality cages and mechanisms to trap wild livestock
-You have 30 stonecrafters and your miners all died with their picks when you had to seal off some clowns with a cave-in and you only had enough metal to make one pick unless you melt your masterwork armor so now there is a huge stone shortage
This suggestion is different from the one made by dudlol. His idea is to modify the manager so that you can have a job that persists until a certain amount of X-level crafts have been made. It gave me this idea.