I know there is a power improvement with Mace cold air intake manifold Insulator to suit Alloytec VZ-VE but is it noticeable?

Assuming that your car is in good working order, then the answer is a definite yes. For more information about product feedback, please check out the link below:

http://www.maceengineering.com.au/epages/shop.sf/en_AU/?ObjectPath=/Shops/mace/Products/MI603