If I were going to do anything with the exhaust, it would be ceramic coating. I don't really like the idea of having a cloth-like wrap on my exhaust that will be getting dunked in muddy water.

For the cold side, there's not really much to be wrapped. Most of it is elbow-shaped silicone couplers going through very tight places. There's only about 1 foot of actual pipe. Similarly, if anything, I might get that pipe ceramic coated along with the exhaust, but I wouldn't expect any noticeable gain from it at all.

If I were to go with water/meth injection, I would set it up like my brother's system on his STi. It automatically starts at a certain boost level, and ramps up to full flow at a higher boost level (the controller for the system has adjustable end points for this ramp up). His stock intercooler water spray is also integrated into this system to automatically start spraying at some boost level (before meth injection starts), rather than requiring a manual press of the button as it does in stock form.

I think an automated intercooler sprayer with a manual override button (to force a spray) might be a nice way to get some noticeable improvements without getting too intrusive or requiring any custom tuning to fully take advantage of it.