1. Bring back item degradation, use an Anvil for full repairs and Field Repair Kits (see below) for field repairs... just don't make items so fragile that they have to be repaired from 0 after every fight like in Oblivion. Tiny xp award. Every Field Repair makes an item degrade faster, while a full repair at an Anvil makes it as good as new.
2. You cannot repair items using a Field Repair Kit (you can't even make the kits) until you have the appropriate materials Perk, you can only use an Anvil.
3. XP is based on complexity and material - Daedric materials are worth a lot more base xp than Iron/Leather. Higher xp for more complicated recipes, lower xp for simple recipes.
4a. Put the Grindstone and Work Bench into the same category as the Tanning Rack and Smelter - no xp.
-OR-
4b. Grindstone and Work Bench award minimal xp in line with repairs.
You have to make a Field Repair Kit yourself and they are worth no xp. A Leather Kit only repairs Leather Armour pieces. An Ebony Kit repairs Ebony and so on. Each kit requires An Ingot, Leather and Leather Strips to make. Whetstones act like single use Grindstones as well as Field Repair Kits. Using a Whetstone on a fully repaired weapon will give it a temporary damage bonus, above that given by a grindstone, which is lost through degradation. Using it on a degraded weapon will only return the item's damage to it's original maximum and make it degrade faster. Whetstones can be found as loot (as abundant as some of the food ingredients) or purchased from a Merchant. Instead of a Whetstone, Bows use Oils. Field Repair Kits, Whetstones and Oils all have negligible weight. Repair xp is half the materials value of the item rounded down (repairing an Iron Dagger is worth 1xp, repairing a Dwarven Battle Axe is worth 6xp).
Forge-use xp is calculated based on material and recipe complexity. Leather, Leather Strips and Iron Ingots are worth 1xp, Steel Ingots are worth 2xp, Dwarven Ingots are worth 3xp and so on. XP awarded is the sum of all the ingredients. An Iron Dagger will only be worth 2xp, while a Dwarven Dagger will be worth 10xp. A Dwarven Battle Axe is worth 13xp (2 Dwarven Ingots at 3xp each, 1 Iron Ingot for 1xp, 2 Steel Ingots at 2xp each, 2 Leather Strips at 1xp each).
The most efficient way to level Smithing would then be by actually playing the game rather than standing around in town. Because you have to repair, your Smithing skill will grow with your character rather than your character growing with your Smithing skill.
Meh. It's not exactly fully fleshed out, but it's an idea, at least, and far better than just saying "nerf it" or "leave it alone".
EDIT: I started this post when there were no replies... I prefer some of the other ideas like making Iron only get you to level 30, Steel to 40 and so on and having the materials available dependant on your character level. Let the above portion of this post serve to show what happens when you over-think things.