In theory misting is good way to increase the capacity of your ac unit. The problem is that as the well water evaporates the minerals in it will collect on your condenser. Then once a month you will have to acid wash the cond. If you could run distilled water your idea would work.

Your best bet might be to get rid of your condenser all together and use a tube type heat exchanger. Circulate water from your well through the exchanger and back to a near by well. You can also use the ground as a heat sink by burying plastic tubing filled with water/glycol and circulating it through the exchanger. If you are near a lake you can do the same with much better results.