I am a huge alcohol injection advocate. Kind of a hypocrite because I still haven't got around to installing one on my Supra, which needs it badly. Now that I am set on getting the AEM unit, and it is gonna have it's own control for alcohol, I am waiting till then to install mine.
But I agree with Steve that you don't need it if you are still using stock turbos. Alcohol injection serves two purposes:
1. Detonation suppression
2. Enrichment
It also is a awesome cleaner. Your intake manifold and valves will be sparkling after using alcohol for a month.
Considering BPU MKIVs need neither of the two main reasons, there is no point. Now if you have a single, I'm of the opinion that you can continue to use the stock fuel system up to 700RWHP so long as you get a big alcohol injection system that can flow 250RWHP worth of alcohol.
The problem (up until now) is that alcohol in large amounts (like 250RWHP worth) has been difficult to tune. This is because most systems basically are on or off. They go from no spray to full spray, at a user set boost point. This causes the car to bog, basically being flooded with alcohol when it starts spraying. Turn down the spray, and the bog goes away, then you don't have the flow you need at 6000RPM and 25psi. Dual stage systems help a bit (half flow at 10psi and full flow at 20psi), but still not what is ideal.
With the AEM unit, it sounds like you can use a fuel injector(s) (alcohol compatible ones of course) to have it come on gradually. Ideally you would want a duty cycle identical to your regular fuel injectors, that starts at say 10psi. You would have maybe 20% flow at turn on, and it would match your air flow as boost and RPM rise. No bog, and plently of flow.