Good idea, and it would benefit our citizens who spend their time in wild. I'd suggest only about 3 Meebles per food item, so each coal can generate 24 Meebles in addition to whatever the food sells for. Obviously, Ultimates' /smelt should not apply to this, but when someone actually uses a furnace to do so (which might be a little harder to implement, differentiating between /smelt and an actual furnace block?).
maybe there should be a "Crafter" job which you get money for brewing, smelting and crafting. i remember that there used to be a brewing job...
well a normal furnace gives you XP, so if the player cooks an item AND gets XP at the same time then give some meebles?
~ @Bloopers
Furnaces don't give any XP worth mentioning. Cooking food items gives one 0.35 XP, whereas killing a zombie gives you 5. The most you can even get from smelting is 1, when you smelt diamond ore, and 0.75, with redstone ore (both ores that aren't worth using Silk Touch on). It's not really worth mentioning.