Pre-turbo water injection often damages the compressor wheel, especially if it is not implimented correctly and/ or if the water injection is not atomising - water can be very destructive - there are pictures on many forums showing damage to compressors done by pre-turbo water injection - it was used in F1 (engine only had to last about 2 hours) or drag racing (rebuild after each run)

There could be a drip tray/ valance under the intercooler to stop exess water from reaching the wheels, i have not found this to be a problem on mine i have it spraying in a fine mist and it does not use a lot of water (i use the windscreen bottle water to save weight)

Ive ran the external waterspray for a couple of years - before i fitted it i did not think it would make a lot of difference, i thought it would only be used on very hot days or after a hard run/ before a race etc

Yes, it works great on a hot day, but it also works well on a cooler day, you can get a lot of heatsoak even on a cool day, the turbo compressing that air can genarate a lot of heat, even on a cool day

As the OP has mentioned, actual experience of doing something is always better than googling it/ reading it - i run a cockpit adjustable electronic boost controller - i found i could run more boost with the waterspray, even if it was not a hot day.
i specifically chose to fit a smaller intercooler on my car, i could easily have fitted one twice as big (almost everybody else did) but it would have been heavier,would be partly "masked" behind the bumper in my build, would have had an increased internal volume (increasing lag) and a larger thermal inertia (takes longer to cool down than a smaller one - not a lot of people know that - bigger must be better, right - wrong!)

Water has incredible cooling properties and there is somthing called the latent heat of evaporation which is one of the mechanisms that give it these properties, the waterspray alloys me to run the smaller intercooler (by choice) which gives all the advantages of the smaller intercooler, and the performance of a larger intercooler with none of the disadvantages (in fact it outperforms the larger intercooler in some areas)

I completely agree that internal water injection has (far) more potential than an external intercooler waterspray, but the external spray is easy to do, and works well especially with an overall temprature management strategy

Internal water injection is difficult to impliment, there is a finite supply of water and adding a large tank is going to add significant weight, if the engine is set up for the water injection, its bad news when the water runs out (one way ticket to detonation city) if its set up for w/o water injection, it won't get the potential and thee is little point in it, its gonna run out at some point, and some sort of fail: safe will be required, the 2-stage boost controller could be used, with it automatically dropping to the 1st (lower) boost setting when the water runs out

Injecting the correct amount of water is difficult, with different boost/ CFMs etc etc and the systems can be basic/ cheap or expensive/ complicated. Apart from the setup difficulties and the water running out, potential damage to the compressor wheel, there can be problems with the spray not atomising, stalling, thermal shock, water condensing in the intercooler, uneven distribution between cylinders (would you want the water to evaporate before it reaches the cylinders, if its purely water)

Its an interesting challenge water is a lot cheaper than some of the other things we inject into engines!

Thanks for the discussion - made me think about my own plans - let us know how you get on