Wrapping the Manifold will just disipate the heat elsewhere, ie to the exhaust valve seats etc and to the head which is not great. Some say its good to wrap some say its bad, controversial.
I hate all this talk of Heat soak etc, its rubbish as soon as the car is moving it is not longer a problem. I have a typhoon K &N on mt ST170 and it never suffers heat soak. Sounds like you have a very poorly ST170 as mine goes very well