Amost Uncirculated? And what about cleaning?

I just recieved a shipment of Peace dollars which were advertised as "Almost Uncirculated". I was a bit dissapointed, as I ordered about 10 of these in May this year, and the ten I got were very clean and beautiful coins. This time, I placed an order for 20, and 13 of them, while they appear to not be "worn down", are downright filthy looking. I assume the AU designator is about wear rather than dirt and such?

So my next question: I bought these mostly to give as gifts to family for birthdays and graduations and such. Would it reduce their value if I cleaned them with baking soda (as in hot water, baking soda, pinch of salt, and a piece of aluminum foil to soak). I've had great success getting tarnish from silver cups and utensils this way... but not sure on a coin if that decreases value at all?