I am considering making my own distilled water misting system ahead of my condenser/compress unit to get more cooling power out of it.  I am planning on triggering it by using a two-stage thermostat inside the living space.  The condenser/compressor unit is a high quality, 12 SEER, scroll-type Carrier unit.  It is only 2.5 tons for 3300/sq-ft which is why I am trying to get more output on hot days.  Has anyone had experience with this?

I would be careful with this one. These units are designed for certain engineering criteria. What type of refrigerant gas is being used? This effects the condensing temperature of refrigerant and the sub-cooling (temp of the liquid comming out of the condenser going to the evaporator)This will then effect the superheat (temp of the gas comming out of the evaporator above it's saturation point). The worst you can do is damage the compressor by  causing it to deal with liquid slugging (it is designed to handle gas only) by too much sub-cooling. You CAN do it, but only under certain ambient conditions that will be cooling the condenser, but not overcooling it. You will have to add sensors to avoid going out of the design range. Also call your water utility and find out what is in your water. If it has high contaminates, sulfur, ect, you might be seriously reducing the life of the unit by bathing it in water which regrettably really isn't just water anymore. It is also illegal to use water in most communities for condenser cooling unless it is recycled (cooling towers, spray ponds,ect). In your situation, keeping the condenser super clean, going to an r-30 insulation in the attic would help you a lot more. As an example, Adding an r-30 to an r-19 attic can reduce tonnage from 4-1/2 ton to a 2-1/2 ton unit.

An easier way would be to determine your temperature constraints and limit the water flowrate to keep yourself safe(safety valve).  Check your head pressure on the coolest day you would use the unit.  Then wait for a day that is just hot enough for you to want to use the water (90*?) and extremely dry.  Play with your water flowrate (Needle valve) and see how it affects the head pressure.  If it does not drop below your cool day pressure, you should be OK.  This would determine your limit RH and dry bulb conditions.  Then just set the thermostat a few degrees higher than this extreme.  This sounds like it could be fun.  As you drop the compression ratio (high side P/low side P) of your system you should see more efficiency and higher capacity on those hot days!