I'd wrap the downpipe, but probably wouldn't bother with the centre personally.
Ebays a good bet for heatwrap, but i wouldn't automatically go for the cheapest, some of the budget stuff is nasty. Did an uppipe a few years ago on a budget and the stuff got everywhere and left my hands itchy for ages.
Recently did my downpipe with this, its much better stuff
http://www.thermalvelocity.co.uk/Exh...ap-/p-105-409/