I do believe reflective tape works, but is best used in conjunction with other heat-control measures, such as exhaust wrap, heat shields, turbo blankets, etc.
I still use my factory turbo heat shield, but had to trim it with an angle grinder to get it to fit over my larger turbo. Header and Up-Pipe are wrapped completely. I might wrap the hot side of my turbo (in addition to using the heat shield) and a short portion of my downpipe, just to keep heat from radiating back up into the engine bay. But beyond 18-24", the downpipe should preferably be unwrapped so that exhaust gasses cool as quickly as possible after leaving the turbo. This will actually promote a higher exhaust velocity through the turbo.
Use of reflective tape on the intercooler and boost tube system is largely going to depend on whether the car is set up with a top or front mount intercooler. You may also want to use the tape on susceptible portions of the fuel system and pre-turbo intake tubing. I used to believe that a hood vent was a better idea when running a front mount, but now I am leaning back towards retaining the hood scoop to direct air down over the back side of the engine (and turbo) to be blown out down and underneath the car, at speed.
